There's not much to go on as the creature was far too speedy to get a picture (probably because it was in that very hot weather we had).
I'm certain it was a wasp, but rather smaller than the common wasp and much slimmer - seemed it had a proper "wasp waist" not as chunky- looking as the common species. Like the common wasp it was black and yellow but the black was very shiny and the yellow looked brilliant yellow, and much more of it - less obviously banded.
Here is a pic off the internet that looked similar, but it was part of someone's blog and I couldn't find the pic on the blog, let alone the species.
The large area of bright yellow was what stood out. I would guess the size about 1- 1 and a half cm long.