A puffer pack of Permethrin 0.487% insecticidal dust which is particularly effective against Wasps. Read Wasp Foam Aerosol above if you can see the nest.
This insect killing powder will rapidly wipe out a wasp nest and 300gms should be enough for at least three wasp nests.
A slightly better buy is the 500gm Rentokil Ant and Crawling Insect Killer Dust for which there is a link below this item. Larger pack with more "puff" for your money. This is the same powder/dust that is used for the 300gm Wasp Killer Dust.
Puff into holes where wasps are entering the ground or air brick, or, if you can see the nest, puff over the total nest and if possible try to get some into the main entrance to the wasp nest, which will be near the base of the nest.