Question......
If say my MOT expires at the end of April but I took it in for a test now and it failed, can I still use the car until the current cert expires.
In other words does the failure note say not to be used until you do required work, I know I can drive it for a booked retest.
Mick
Difficult ... if it has failed an MOT it could be argued it is not fit to be on the road, and it is the drivers responsibility to ensure his vehicle is "roadworthy" at all times. If you know its failed you know its not roadworthy. The failure is also on the MOT computor, to which the police (and ANPR Cameras) have acces, so the number of excuses to Mr Plod is extremely limited.
IMHO, although this is the legal position as I understand it, it might depend on the reason for failure, somethings are far more important than others.... and life is the most important .... do you really want to risk yours - and others - by driving an unroadworthy vehicle 
Just my thoughts .... dons tin hat and hides ... 
Whilst accepting your points, in my experience, VOSA disagrees.
An MOT is valid at the time of test only and thus a car which passed can fail an equivelant test 5 minutes later - duff lamp etc....
Accepting that serious rust or wear takes time to manifest itself, the 12 month standard certificate is valid for that time. Its a moot point that it can (and often is) effectively revoked by the issue of a roadside form PG9 (VG9) by Police or VOSA requiring removal from place of issue by means of a full lift and retest within 14 days. The retest is the issue of a brand spankers new MOT cert for 12 months, unlike a VDRS scheme form which only tests specific items.
In general day to day use, a ticket is valid until expiry, irrespective of any retest at the owners behest, PG9 issue not withstanding....