Mark,

nice straight dig like that mate just mass fill the founds till about 150mm below F.G.L.

It will be around 16m3, which you should get around 65 quid per m2 at that amount. Thats about £1040. If you think about it, you will have to put at least £350 in concrete anyways, plus about 350-400 quids worth footing blocks, then sand cement and labour! Its not worth the hassle. We always mass fill if the situation allows it!