Could anybody please tell me the name of this block? Although the picture may not show this very well, it is actually made up of three colours. The four corners are a different colour yellow to the centre square + smaller squares. Any help would be appreciated.

Interesting block. I'll be watching for more info.

Four plus one? Maybe not, the 'one' block is different colors.

I would call it a 9 patch variation.

Looks like Four-In-Nine-Patch. Variation of Nine-Patch. The four patch squares form chains that criss-cross across the quilt. A Liz Porter design possibly?

I agree with Nine Patch variation

A 9 patch variation. This link calls it a "4 patch in a 9 patch"

[url]http://www.flickr.com/photos/sylvienoel/5458331127/[url]

Definitely a 9-patch variation. Liz Porters design from 1991 for the Four-in-Nine-Patch has the 'chains' criss-crossing with the same colored fabric just as your block does.