Thanks for the answers!

@Sarg; yes it might been rebarreled, but this rifle which is very similar also have Metford rifling, but it does have proof marks:

http://www.highwoodclassicarms.co.uk/Firerms%20For%20Sale/smlec.htm

I'll let a gunsmith look at it this weekend before shooting it.

@Nailcreek; From what I can see the front and rear sight looks to be standard Lee Speed but I might be wrong?

Cheers,
Lars