DVSA Fines a Berkshire Garage £1,600 for Pops and Bangs

• A Berkshire garage, SVG Motorsport Ltd, has been fined £1,600 after a joint DVSA and Thames Valley Police undercover operation caught it fitting illegal “pop and bang” exhaust modifications.
• The firm removed a customer’s catalytic converter and remapped the engine without saying the car would become illegal to drive on a public road.
• It is the third tuning shop in the Slough area the DVSA has prosecuted for the same offence, after two earlier cases in 2023 and 2024, and a garage convicted of it can face an unlimited fine.

A Slough Tuning Shop Is Fined After Undercover Officers Expose Illegal Mods

SVG Motorsport Ltd, trading as SVG Performance from premises in Taplow, near Slough in Berkshire, pleaded guilty at Reading Magistrates’ Court on 14 August to fitting an illegal “pop and bang” exhaust modification. The case followed a joint investigation by the Driver and Vehicle Standards Agency (DVSA) and Thames Valley Police, in which undercover officers posed as ordinary customers booking work on a car.

Investigators found that the garage had removed the vehicle’s catalytic converter and remapped its engine control unit to make the exhaust bang and pop on deceleration and gear changes. The DVSA said SVG Motorsport did not tell the undercover customer that the work would make the car illegal to drive on a public road, or that it would fail its next MOT test. The court ordered the company to pay a £200 fine, an £80 victim surcharge and £1,320 in compensation, a total bill of £1,600. A garage convicted of this offence can be fined an unlimited amount, set by the magistrates hearing the case.

“Pop and bang” work gets its name from the loud crack a car produces when unburnt fuel ignites in a hot exhaust system as the driver lifts off the throttle or changes gear. Garages that offer it usually strip out the catalytic converter, which would otherwise filter much of that unburnt fuel and the pollutants in it, and then alter the engine’s software so the fuelling pattern that produces the noise happens on demand. The result is a car that sounds, to some owners, more exciting to drive. It is also a car that no longer meets the build standard it was approved against, produces far more pollution than it is legally allowed to, and is far louder than the limits that apply to the vehicle when it was tested for road use.

Thames Valley Police’s involvement points to how this type of case is usually built. A single undercover visit, in which an officer simply asks for the modification as a paying customer would, can produce enough direct evidence of the garage’s working practices to support a prosecution without needing to track down every previous customer. The DVSA has used the same approach, working with different police forces, on a number of “pop and bang” cases in recent years, and those cases keep landing in Berkshire and the wider Thames Valley area.

Why This Hits More Than the Garage Itself

The DVSA’s Market Surveillance Unit (MSU), which led the investigation alongside Thames Valley Police, exists to stop unsafe or illegal parts and modifications reaching UK roads. Its head, Chris Dormand, said there were “no excuses” for businesses that carry out the work. “DVSA works tirelessly to stop pop and bang modifications, removing antisocial noise and excess pollution from our streets,” he said. “DVSA will target any businesses who flout the law, as demonstrated by the success of this prosecution.”

The person who pays for this kind of work is not just buying a louder exhaust. A car with its catalytic converter removed and its engine control unit remapped in this way no longer meets the roadworthiness standard it was built to, and driving it on a public road becomes an offence in its own right. It can also fail its MOT outright, and an insurer could refuse a claim if the modification was not declared on the policy. The driver, not just the garage, carries that risk.

Police officers stopping a car with an obviously modified exhaust have the power to issue a roadworthiness prohibition on the spot, which takes the vehicle off the road immediately rather than waiting for its next scheduled MOT. A driver pulled over this way does not get to choose when the problem is dealt with, and the cost of reversing the modification, refitting a catalytic converter and restoring the original engine software, falls on them, not on the garage that carried out the work in the first place, unless they are willing to pursue the business separately for a refund.

A Pattern, Not a One-Off, in the Same Few Streets

SVG Motorsport is the third business in the Slough area that the DVSA and Thames Valley Police have prosecuted for fitting illegal “pop and bang” modifications, after AET Motorsport in 2023 and Onyx Performance in 2024. Three separate convictions in the same small area over three years point to a local cluster of demand for the modification rather than a single rogue trader, and the DVSA’s enforcement record shows it returning to the same streets to find the next one.

Nationally, the MSU’s wider work covers a steady flow of reports about unsafe or illegal vehicle parts and modifications from members of the public, trade bodies and manufacturers, which its officers then investigate and, where the evidence supports it, refer for prosecution. The unit also attends trade events to talk directly to garages, retailers and suppliers about staying on the right side of the rules, rather than relying on prosecution as the only tool it has.

What the Fine Actually Costs, and What It Does Not Cover

The £1,600 total SVG Motorsport must pay breaks down into a £200 fine, an £80 victim surcharge and £1,320 in compensation. That figure is a one-off penalty on the business, not a cap on what a future case could cost. The offence carries an unlimited fine, so a magistrate hearing a repeat case, or one involving more vehicles, can set a far higher figure, and a company with previous convictions for the same conduct would expect a harsher sentence than a first-time offender.

None of that £1,600 compensates a driver who unknowingly bought the modification and is now running a car that can fail its MOT or invalidate a claim. There is no separate refund route built into this prosecution for that driver, who would need to pursue the garage directly, through a small claims process or the Motor Ombudsman, to recover the cost of undoing the work.

What to Check Before You Book an Exhaust Modification

Anyone having exhaust or engine work done can ask the garage directly whether it will affect the car’s MOT status, its emissions compliance or its insurance, and get the answer in writing before booking the job. A straight answer that the work keeps the catalytic converter in place and does not remap the engine for extra noise is the safest sign the job is legal. Drivers who believe a garage is offering or has already carried out this kind of illegal modification can report it to the DVSA’s Market Surveillance Unit, which handles exactly this type of intelligence.

Anyone who has already had similar work done and is unsure whether it is legal can ask an independent garage to check the exhaust and engine control unit against the car’s original specification before its next MOT is due, rather than finding out at the test centre. A dealer selling a used car with an aftermarket exhaust fitted should also be able to show that the system still carries a catalytic converter and meets the noise limit set for the vehicle, and a buyer is entitled to ask for that in writing before signing anything.

Sources:
Driver and Vehicle Standards Agency, prosecution of SVG Motorsport Ltd, Reading Magistrates’ Court, 14 August 2026.
Driver and Vehicle Standards Agency, Enforcement Sanctions Policy, gov.uk.