http://www.bailii.org/ew/cases/EWCA/Civ/1999/1311.html
In Dimond v Lovell (House of Lords 2000) it was found that where a vehicle is off the road due to negligence of a third party it was reasonable for a person to be supplied with a like for like replacement.
It has been implied that in the case of a licensed taxi or private hire vehicle that the local authority would not treat the owner fairly if they did not allow a replacement vehicle to be used if the original was off the road in such circumstances. Several councils do allow temporary transfers whilst the original vehicle is being repaired, subject to the replacement meeting all the conditions of license. (insurance, mechanical, MOT etc.).