Ok im more familiar with US helmets
Yes you can see the bolt in the top as said in the thread it had a 1940 rotted liner in it, so it was also used in w.w.2, but still a good little helmet. Militarymania, you will find it is a Mk1 as the helmet you discribe with no edge, ie a raw edge is an A Patt helmet,
brought out in 1915 ish, the mk1 is the first brodie with a rim.
Nice find Dave ! Im sure its a Brodie re-worked for ww2. I think those stress marks on the forming of it seem to be common on ww1 lids.