A loud can, an LED bulb, a tail tidy and a small plate are the four most common changes made to a used motorcycle in the UK, and each one is judged by two different rulebooks. The MOT tester works from the DVSA inspection manual for motorcycles, last updated on 1 April 2026. A police officer works from the Road Vehicles (Construction and Use) Regulations 1986. They do not agree, which is why a bike can pass its MOT on Monday and be stopped on Tuesday. This guide sets out what each says, and what a buyer can read off the free MOT history before viewing. The checker on this site covers cars, vans, motorcycles and lorries.
The MOT answers one question: on the day of the test, did the bike meet the minimum standard in the manual. The manual is deliberately narrow and says nothing about anything outside its list. Construction and Use says what a vehicle must be like every time it is on a road, and it is enforced by police and DVSA officers, not testers. So an exhaust can pass section 8 of the manual and still be an offence under regulation 57B. Where this guide says "passes", it means the MOT and nothing more.
Section 8.1.1 of the motorcycle manual is short. The tester should assess the noise by revving a warm engine to approximately half its maximum speed, and the system should be in such condition, or of such a type, that the noise is not clearly unreasonably above the level expected from a similar motorcycle with a standard silencer in average condition. The defect, noise levels in excess of those permitted, is Major. There is no figure, no meter and no test track. It is one person's ear against their memory of the standard bike, and on a twist and go scooter the tester cannot rev the engine at all.
A well made road legal aftermarket system will usually pass. A race can with the baffle removed usually will not, and a tester who is unsure tends to fail rather than pass, because their own licence is on the line. The one thing that is not subjective is section 6.1.2(c): a silencer marked NOT FOR ROAD USE, TRACK USE ONLY or similar words is a Major fail regardless of how it sounds. Race cans are stamped that way because they were never put through noise approval, so the marking does the tester's job for them. The removable baffle itself is not a defect. A can with the baffle in and no track marking is tested as it stands. What the manual cannot see is that the baffle comes out again in the car park, and that is what the roadside rules are for.
Under regulation 57A, a replacement silencer on a bike first used on or after 1 January 1985 must be built and marked to the relevant standard, in practice the British Standard or EU approval mark cast into the can. Regulation 57B makes it an offence to use a bike altered so that it is materially louder than it would be in standard working order, and regulation 97 bans avoidable excessive noise from any vehicle. These are Construction and Use offences under section 42 of the Road Traffic Act 1988: a £50 non-endorsable fixed penalty under the Fixed Penalty Order 2000 as amended in 2013, or up to £1,000 in court. No points, but a rectification notice and a second stop can follow.
Here the motorcycle manual is more lenient than the car manual, and most advice online is written for cars. The car manual, section 4.1.4, says halogen headlamp units on vehicles first used on or after 1 April 1986 must not be converted to HID or LED bulbs, and a converted unit must be failed for light source and lamp not compatible. The motorcycle manual has no equivalent sentence. Its section 4.1.4 requires white, yellow or mainly white with a blue tinge, intensity not significantly reduced, and defines a light source as any bulb, LED or other means of emitting light. Section 4.1.2 then requires the dipped beam cut off between 0.5 and 2.75 percent below horizontal for a lamp centred at 850mm or less from the ground, with the kick up visible. So an LED bulb in a halogen reflector is not an automatic fail on a bike. It passes only if the beam is still a proper European dip the tester can aim, and a cheap bulb in a reflector built for a filament usually scatters light above the cut off and fails on aim instead. For a buyer, a headlamp aim fail after a clean pass the year before is often a bulb change, not a fork problem.
Indicators are where tail tidy kits fail. Section 4.4.3 requires amber light and a minimum separation between the illuminating surfaces of 240mm at the front and 180mm at the rear on a solo motorcycle, 240mm and 160mm on a moped, and 400mm at both ends with a sidecar. The tester does not measure and rejects only what is obviously wrong, but micro indicators tucked under a shortened tail often are. Flash rate must be 60 to 120 per minute; a fast flash after fitting LEDs is Minor, recorded but not a fail. Sequential indicators are expressly not a reason to fail.
Two more things go missing with a tail tidy. The rear plate must be lit whenever the position lamps are on, so a plate lamp wired out is a Major fail under 4.7.1(b)(ii) if it was the only one. And the manual requires one red rear reflector on the centre line and says in terms that reflective tape is not an acceptable substitute. Plenty of tidies ship with a sticker where the reflector used to be. It does not count.
The tester inspects the rear plate only. Under section 0.1, a plate must not be obscured, damaged or delaminated, must not have background overprinting or tints and films over the characters, and on a bike first registered on or after 1 September 2001 must not have a honeycomb background. Characters must be the right size, stroke and spacing, in the prescribed font or substantially similar, not italic or broken. Rear plates on motorcycles must be two lines, with three lines and larger 89mm characters allowed only on bikes first used before 1 September 2001. On a plate fitted on or after 1 September 2021 every character must be a single shade of black, so two tone and carbon effect characters are out. Imported bikes with no room for a standard plate can carry a smaller one. The tester does not measure and rejects only what is obviously incorrect. All four plate defects are Major.
GOV.UK adds the roadside side. A motorcycle registered on or after 1 September 2001 must display a plate at the rear only; older bikes may carry a front plate but do not have to. A plate fitted after 1 September 2021 must be marked BS AU 145e and show the supplier. The penalty for an incorrectly displayed plate is up to £1,000, on top of the MOT fail. A small plate is the modification most likely to be let through by a tester who is not obviously bothered and then picked up by an officer who is.
Two absences surprise people. First, there is no emissions test in a motorcycle MOT. The car manual has a full section on exhaust emissions with metered limits. The motorcycle manual has section 3 marked "not in use" and section 8 covering noise only. A decat pipe or a remap is invisible to the test. Second, mirrors are not inspected. The motorcycle manual has no mirror section, so bar end mirrors, one mirror or none at all make no difference to the certificate. Neither absence makes the modification lawful or sensible. It just means the MOT is not where it will be caught. For the longer list of things the test never looks at, including engine, clutch and service condition, read what the DVSA data says really fails a bike.
| Modification | MOT outcome (motorcycle manual, April 2026) | Roadside position |
|---|---|---|
| Aftermarket road legal can, marked, baffle in | Passes if not clearly louder than standard (8.1.1) | Lawful if marked to standard under reg 57A |
| Same can, baffle out | Major if clearly too loud at the test | Offence under reg 57B, £50 fixed penalty, up to £1,000 in court |
| Race can stamped NOT FOR ROAD USE | Major on the marking alone (6.1.2(c)) | Not marked to standard, offence under reg 57A |
| LED bulb in halogen headlamp | Not an automatic fail on a bike; must give correct colour and aim (4.1.2, 4.1.4) | Depends on the lamp still meeting lighting regulations |
| Micro indicators on a tail tidy | Major if separation obviously under 180mm rear or 240mm front (4.4.3) | Same separation rule applies |
| Fast flash after LED indicators | Minor only (4.4.4) | Rarely enforced alone |
| Reflector replaced with tape | Fail; tape is expressly not acceptable (4.8) | Mandatory reflector still required |
| Small or show plate | Major only if obviously wrong (0.1) | Fine up to £1,000, GOV.UK |
| Decat, remap, mirrors removed | Not inspected | Not an MOT matter; other rules may apply |
This is the part only a history checker can show you. Every defect is recorded in the manual's own wording with its section number, and it stays on the public record. A line reading "Exhaust noise levels in excess of those permitted (8.1.1 (a))" tells you the bike was presented with a loud can. "Number plate does not conform to the specified requirements (0.1 (d))" tells you about the plate. "Headlamp emitted colour or intensity not in accordance with the requirements (4.1.4 (a))" is very often a bulb. Testers also add free text advisories, and "exhaust modified" appears more often than sellers would like.
The pattern to look for is the fail and the fast pass. A Major on noise, then a pass on the same or the following day with nothing else changed, means the standard can went back on for the retest. The retest is free if the bike is left at the station and retested within ten working days, so this costs the seller nothing and is routine. It does not make the bike a bad buy. It does tell you that "road legal exhaust" in the advert needs testing with your own ears, and that you should ask whether the original can is included. The reverse matters too: a bike with a clean record and a race can in the photos has probably never been tested with it fitted, so the certificate says nothing about how loud it is.
Run the registration on the free MOT history check, read the defect wording section by section, then read how to read the gaps in a bike's record, because a modified bike is often also a summer only bike and the two patterns overlap. The buyer scorecard counts repeated advisories for you.
An MOT pass tells you the tester did not think the bike was clearly louder than standard on the day, found no track marking, could aim the headlamp, and saw nothing obviously wrong with the plate and the indicators. It does not tell you the bike is lawful on the road, because the MOT does not measure noise, does not test emissions, does not look at mirrors and does not get a ruler out for the plate. If you own a modified bike, the cheap fixes are the ones that actually get caught: put a real reflector back, wire the plate lamp in, fit a two line plate to BS AU 145e, and keep the standard can. If you are buying, read the defect lines with the section numbers and trust the pattern over the advert. Most of the time the modifications are harmless and the paperwork is fine. When it is not, the record usually says so.
Sources: DVSA MOT inspection manual for motorcycles, sections 0.1, 4.1, 4.4, 4.7, 4.8, 6.1.2 and 8.1.1, updated 1 April 2026; DVSA MOT inspection manual for cars and passenger vehicles, section 4.1.4; Road Vehicles (Construction and Use) Regulations 1986, regulations 57, 57A, 57B and 97, legislation.gov.uk; GOV.UK, Displaying number plates; Road Traffic Act 1988 section 42; Fixed Penalty Order 2000 as amended 2013. Figures checked 11 September 2026.
MOT Check UK is built and run by Jagat IT Limited, a software and automation company working with UK businesses.
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