Just a case of trying really Chippie. It's a chunk of chipboard on a couple of brackets masquerading as a breakfast bar. If it was the footings to an extension then...
I'm not trying to denigrate the OP I just misunderstood from his description what he was trying to achieve.
He did say breakfast bar, I just happened to catch the bit about 400 deep. It's only Tuesday and I'm zonked...so reading at a slower pace with a more boring frame of mind!
Sorry guys - yep it's basically a big shelf. 400mm projecting out off the wall for a 1.5m length. so I'll space the brackets at 0.5m and 1.0m. There's a 6mm pre-drilled hole in the brackets so I'll give the 6mm thunderbolts a go.