What spider is this?

What spider is this?

Observation - What spider is this?. Description: Large brown spider found under a piece of wood in my garden. With legs spread, it was about the size of a 50p piece, with a very large abdomen. I am in the South of the UK. Any ideas what it is?

Large brown spider found under a piece of wood in my garden. With legs spread, it was about the size of a 50p piece, with a very large abdomen.
I am in the South of the UK.
Any ideas what it is?