No4 Mk1 T sniper quick detach scope mount stuck

[Lee Enfield]

That sounds unusual, isn't the rear sight supposed to be clearanced to allow removal of the bolt without dismounting the telescope?

Never seen one in person - well over 100 No4Ts in my hands...

only (ever) seen photos of 1 on the internet, except for a couple done obviously wrong, by grinding on the leaf itself..

I believe it was not very common in service, or a very late addition.