I have just checked with VOSA and there is good news and bad news......
If a vehicle fails an MOT test (Or prior to an MOT), you are allowed to drive it to and from a place of
repair without a valid MOT certificate providing you drive it
DIRECTLY there and back again. I am not sure how that would affect you with, what could be considered, non-essential work, such as electronic ignition.
However, VOSA did tell me that if you take your car for an MOT test, prior to an MOT expiry date, although VOSA would still consider that the remaining MOT was still valid, the police might not and if you continued to drive the vehicle on the old MOT certificate, they might consider that you are driving an unroadworthy vehicle and
could impound and crush your vehicle.

Dont know if that helps or not?