Thanks John,
Just been shooting it and TBH it is so easy to cock and (especially as it is really my eleven year olds' ) I might just leave it as it is now after all this - shoots really nice and knocks over anything it has to and smooth as silk with the original maybe slightly tired spring.
I changed the spring in my Mk I for the Chambers one as that was a bu**er to cock (even more than normal) and the spring was about 4 coils over spec - bearing in mind my Senior going kaput I wanted to make sure the Mk I was not oversprung and it's definitely easier now.
You have to love these old Webleys - so easy to strip in seconds, build quality is awesome and so much fun to own and shoot.
Max; looking for: Baikal IZH 61 side lever rifle