We had a massive wasps nest in a house we moved into a few years ago. Got a pest control guy out, he said it was the biggest one he’d ever seen (nearly 3 foot across) and used a blower thing to kill everything with an exoskeleton in the roof space. Charged us about sixty quid I think, but sorted the problem straight off. If you’re worried about it get a professional in.
Although stwhannah’s suggestion is pretty sound too:
Ant powder containing Permethrin. Nasty stuff, but very effective.
It’s not *that* nasty. I mean, don’t sprinkle it on yer chips like, but it’s also a standard medicine available over the counter in UK pharmacies for slapping directly onto your skin for certain, er, infestations – if you read the instructions and do what you’re told it’s not likely to kill you…