If they are paper wasps as cats-back has suggested then you can put a firelighter on the end of a long stick, light it and wave it under the nest... 

It's not the kindest thing to do, but it does disarm them and makes it possible to destroy the nest.

ah yes, I googled and it seems they are paper wasps. Clever little things:)

Got the "getting rid of" under control. No, I'm not a piromaniac. Wasps spray does the trick

Now lets see if surface spray stops them coming back

Thanks everyone for your help

Ive always just knocked the nest down in late afternoon and sprayed surface spray in the area it was being built

They hate WD40...and won't return to nest

LOL :^O