Long story but worth telling:-
When I brought my gen 5 in January it had a recent MOT fail and a pass from a week later, from October 2012.
A few weeks after buying I took the car to a garage because I needed someone to certify that it has an alarm, for my insurance company.
The only way the garage would do this was if I paid them something. They wanted £20 but as they were advertising MOTs at £25 I took one of them instead, thinking that I would push my MOT expiry back a few months with the extra fiver.
With hindsight it was predictable that the car would fail and it did on the same things the first of the original MOTs failed on. Maybe the repairs that got it throughout the MOT the second time weren't done very well?
Anyway, I'm now in a dilemma - I've got the MOT pass which the car came with, which is valid until October, and a more recent fail. Is the car road legal? So I rang VOSA and they confirmed that as long as a car has an in-date MOT it is legal until it expires and it is not superseded if you have another MOT that fails in the meantime.
The fails are now being repaired (for the second time, I presume) in preparation for October's re-test.