That's a nice, almost complete set. The Hawks don't seem to be very sought after, which is a shame. They were never a very robust rifle, so ones in good condition seem to be scarce. With the box and accessories, I'd say the rifle is worth about £90-100, but you may need to come down a little because the box doesn't have the card sleeve, and there's no instruction manual with it.
I sold a boxed MkIII Hawk on here for £125, and 3 good condition, unboxed Hawk MkII's for £220 for all three.
http://www.airgunbbs.com/showthread....-1970-s-Webley
http://www.airgunbbs.com/showthread....kII-Collection