You get some mad forts in Ireland. This one for instance ...

http://www.megalithomania.com/irishgenius/zCregduff.htm

I think that there were probably just the same sort of monument in England et al, but intensive farming (still to really reach Ireland) has erased them.

The layout you describe would fit well with a lot of Irish sites, but the 40m gap would be a huge one even in the largest over here. Something that large would tend to have a stone fort in the centre.