Swapping an engine — whether for performance, repair or replacement — is a significant modification that carries legal requirements in the UK. Failing to notify DVLA of an engine change is an offence, and the V5C registration certificate must accurately reflect the vehicle's specification. In 2026, here is what you need to know about engine swaps and the DVLA notification process.
Do You Need to Notify DVLA?
If the replacement engine is fundamentally the same type as the original — same fuel type, similar capacity and performance — you may not need to formally notify DVLA, though updating the V5C is still good practice. However, if the new engine differs from the original in any of the following ways, formal DVLA notification is required:
- Engine capacity change: Even a small change in engine displacement requires notification
- Fuel type change: Converting from petrol to diesel, or adding an electric motor, always requires notification
- Power output change: A significant increase in engine power may require VOSA Individual Vehicle Approval
- Emissions standard change: A different Euro emissions standard affects the vehicle's tax band and MOT requirements
DVLA V5C Notification Process
To notify DVLA of an engine change, you must complete the following steps:
- Obtain supporting documentation: Get the engine number, engine code and any relevant technical documentation for the replacement engine
- Complete the V5C/2 form: This is the notification of a vehicle alteration form
- Provide evidence: DVLA may require a letter from a garage, engineer's report or other evidence of the engine swap
- Submit to DVLA: Send the completed form and supporting documents to DVLA
- Receive updated V5C: DVLA will issue a new V5C with the updated engine details
Road Tax Implications
An engine swap can change the vehicle's CO2 emissions figure, which directly affects the road tax band. This is particularly significant when swapping to:
- A higher-emission engine: Road tax will increase, potentially significantly for older high-emission engines
- A lower-emission engine: Road tax may decrease, potentially saving hundreds of pounds per year
- A different fuel type: Alternative fuel vehicles pay a reduced standard rate of road tax
The new road tax rate applies from the date the V5C is updated. The DVLA will recalculate the road tax band based on the new engine's emissions figures.
MOT and Engine Swaps
The MOT test does not directly verify that the engine matches the V5C, but an engine swap can affect MOT outcomes:
- Emissions testing: The replacement engine must pass the same emissions test as the original — if the swap results in higher emissions, the car may fail its MOT
- Engine management systems: The replacement engine's ECU and emissions systems must be fully functional
- Fuel system integrity: All fuel lines, tanks and injection systems must meet safety standards
Insurance and Engine Swaps
An engine swap must be declared to your car insurance provider. Failure to declare a significant modification — and an engine swap is a significant modification — can invalidate your insurance policy. Notify your insurer:
- Before the engine swap if possible, or immediately after
- Provide the engine details including code, capacity and fuel type
- Obtain written confirmation that the modification is accepted
An engine swap that increases performance may increase your insurance premium. An engine swap that reduces performance — such as fitting a smaller engine — may not affect the premium but must still be declared.
Performance and IVA Requirements
If the engine swap significantly increases the vehicle's power output or performance, the car may need to be re-submitted for Individual Vehicle Approval (IVA) testing. This is particularly relevant for:
- Engine swaps that increase power by more than approximately 20-30 percent of the original output
- Vehicles that are close to power thresholds for vehicle categories or insurance groups
- Classic cars with non-standard engine installations