Hiya...just butting in, because I actually work for DEFRA! :-)
As far as boosters go, your pet must be administered booster vaccinations in accordance with the vaccine manufacturer's instructions. So if the original vaccine advises a booster every year, then you must do it. Some vaccines, however, are good for up to 3 years, so it all depends. Therefore, your original vaccine is probably still good, but you'd have to ask the vet. The intial rabies vaccine MUST be given AFTER microchipping!!
You will need to wait 6 months from the date of the ORIGINAL blood test before entering the UK. So long as the animal is boostered on-time with accordance to what I outlined above, no further blood tests are needed.
Not to rain on your parade, but e-mailing DEFRA will not get you a waiver. Waivers are only granted in EXTREME circumstances.
Feel free to PM for further advice. I cannot issue "official" advice on a forum like this, but I can tell you what I know in my capacity of answering queries very similar to yours on a day-to-day basis :-).
EDIT:
Sorry, I failed to realise that your vet didn't actually do the intial rabies vaccine after microchipping...I thought you were referring to boosters after the initial PETS process is completed. Please read my reply to Yael below for clarification!!