I knew it would be a numpty moment. I was missing a where clause, so trying to do a top 10 over the entire dataset(?)
DECLARE @g geography = 'POINT(-1.43499 52.53194)';
SELECT TOP(10) *
FROM info.Roads
where street.STDistance(@g) < 5000
ORDER BY street.STDistance(@g);
It now takes 0 seconds to run and the Execution plan now comes out completely different