How many new houses are built to that size though? The UK has a lot of very old housing stock.

Quite a few, though it may have crept up slightly - one link I found said the Uk average new builds size 2002-2012 was more like 1030 sq ft.

UK new build houses (as a type - of course there's lots of variety) are a strange breed. Small and crammed into tiny lots though cleverly designed to make the most of a small space. Energy-efficient but shoddily constructed. The cheapest premium-looking materials (i.e. brick). Generally nice enough to live in but a bit depressing.