Wouldn't it be more complicated for you in the USA as it has a bore over .5" diameter so would be classed as a "destructive device" and subject to strict controls?
I'm sure this rifle would be a good buy as in investment in the UK, as it is in working condition, and they definitely aren't going to make any more of them.
There were loads of "deactivated" guns for sale at Beltring, which have a number of modifications to render them un usable. These can be bought by anyone in the UK with no need for permits etc. Some of them were obviously worn out junk, as they are no good for shooting they have been turned into display pieces. However, there were some really nice ones there as well, like WW2 USGI Issue M1911A1 pistols made by US Switch and Signal Co. in almost brand new condition. These were being sold for nearly 700 each. I would much sooner these could be legally owned as live pistols in the UK.