I can't be sure. I've trawled the internet and the closest I can get to it is Ectemnius continuus. Continuus seems to have the same stripe pattern on the abdomen. What worries me is that most photos of that wasp show dark fibular sections of the legs whereas your photo seems to have completely yellow legs. Then I found this:
If you look at the 4th photo for continuus the front 4 legs do look almost completely yellow whereas this is not the case in other photos so I'm not sure how significant this is.
Hope this helps,
Thanks Alan! Whow, these photos in flight with a prey are really impressive!
Well I also don't know how relevant are the colours of the legs. I only can list here the species recorded in Spain:
Ectemius borealis, E. cavifrons, E. cephalotes, E. confinis, E. continuus, E. crassicornis, E. dives, E. fossorius, E. guttatus, E. hispanicus, E. hypsae, E. kriechbaumeri, E. lapidarius, E. lituratus, E. massiliensis, E. meridionalis, E. nigritarsus, E. palamosi, E. rubicola and E. sexcinctus.
Alan - Wow! I echo Isidro's comments on the fantastic in-flight photos on the page you give the link for. Reminds me of Stephen Dalton's in-flight work (eg. http://www.stephendalton.co.uk/photo_1240801.html).