Matt,
I am sorry to hear that you live in the UK... Getting it deactivated will definitely lower the value in the rest of the world, but in the UK, you will be fortunate if the authorities will even allow that at this late date... they may just confiscate it... I hope not. Someone who can surely advise you on this matter is a fellow member that lives in the UK. His screen name is Tacfoley. Do a search for posts by him and send him a private message. The link is in the top right hand corner of each page of this site... and so is the search link...
He was required to eliminate a lifetime of a gun collection when they were banned in the UK... he is painfully aware of the law and the consequences...
If you go to our homepage
http://www.lugerforum.com and visit the Member Gallery, you will find a photo essay created by Tacfoley on the actions taken by your government to deactivate one of his favorite Lugers... the pictures tell a story that is tantamount to nothing less than the destruction of a piece of history... If you are allowed to retain this Luger, it will have to undergo the same permanent unreversible surgery that emasculated his Luger...
Good Luck and post photos of what your Luger looks like and the markings if you get the chance...
with sincere regrets for your situation,