If a vehicle breaks down on the highway or roadside, the vehicle owner/user can arrange for roadside assistance from a breakdown service, or have the vehicle collected.
If simple repairs can be done quickly, without the need to dismantle or remove vehicle components, and where there is no risk to other road users or the public, then this is perfectly reasonable.
You can repair your own vehicle on private land unless the repairs are for gain or profit. Works should only be carried out by an experienced person. Significant work and dismantlement should only be undertaken on a licensed premises.
Regular repairs and renovation projects may be seen as antisocial, and can impact on local residents, the public and the environment.
If repairs or dismantlement causes environmental or highway hazards such as oil spills, excessive noise, debris, fumes, or where vehicle repairs are part of a project or business/service, then this is an offence under the Clean Neighbourhoods Enforcement Act 2005 and can carry on the spot sanctions as well as prosecution of up to £2500 at court.