You are not required to surrender your MOT certificate before presenting a vehicle for test. It therefore follows that a failure does not invalidate the existing certificate.
It would be interesting to access the information on the VOSA website, though, which you can do with your VIN and reg number. It will then tell you the status of the MOT. It will come up with the last reasons for failure, but will it also come up with an indication that an MOT is still in force?
I can say just one thing about this that I am now absolutely certain - the law is an ambiguous ass: I have recently received wholly unjust and inflated court costs over a case I was pursued for where I merely asked to clarify an ambiguity in law. The law is what the judge on the day thinks it should be. Where there is an ambiguity, the law is simply random and statute offers no meaningful guidance. If you do what you think is sensible, this is your only guide. If your car fails on headlight aim and you drive home in daylight, so what. If your car fails because the emissions are out, not so important but get it fixed quick. If your car fails because there is a tyre worn to the carcass, it makes no sense to drive it at all and you should be sent to the clink if you use it [as far as I am concerned!].
We, sensible folks, need to go about our reasonable business. Just do what is sensible. The police, courts, councils, traffic wardens and home office with their mechanised fine-distribution cameras, and VOSA with their computerised road licence fines and 'continual insurance' scams will turn your life into hell in this police state as readily as they can, seemingly just so that they can all then say how important their public-servant jobs are to keep the horrible general public in check. Do what is right, but be warned that this may not be enough and random fines and prosecutions for traffic offences you may never have heard of before will occasionally land in your lap. You can't avoid it. Big Brother is watching, and he's out to get YOU!
