As I am apparently a professional pest controller (I’ve got a certificate that says so and a white van full of toxins on the driveway) I feel duty bound to say get a professional in. The cost for dealing with a wasp nest should be around the £50 mark. Sounds a lot but then you are paying for somebody to turn up with the right equipment and pesticides etc and take the risk of being stung whilst up a ladder (never underestimate the ability of wasps to form a swarm if they detect they are under attack). Some of the over the counter stuff is good but the pesticides a pest controller is able to get hold of are much more specifically formulated (they usually have a stronger concentration of the active ingredient and may include other compounds that have the benefit boosting the active ingredients efficacy).
If you feel you should be able to tackle it yourself the wasp killing aerosols are good but make sure you buy a decent quality one. Digrain is a good brand to look out for. The powders available are very good but can take a while to finish a nest off (the upside is they are less likely to agitate the wasps whilst they kill them). The powder I use is formulated to attack the nervous system of the wasps and is slow acting but ultimately successful. It is also formulated to remain lethal for longer that the commercially available stuff. Diatomaceous Earth, if you can find it, is a possible alternative. It slices the wasps to pieces at the same time as dehydrating them to death and has no known insect resistance.
One chap once told me how his dad had tried to get rid of a wasps nest by sticking a burning stick into it. Once it had set fire to the nest, the shed it was in and the garage that was close by it did indeed get rid of the wasps…