UAVs don't have magic powers as far as I know - they're a target for air defence systems like any other aircraft. They've been shot down before and will be again.
Assuming you've got adequate air defence.....
https://news.yahoo.com/british-tanks...124411826.html
....
"Were the British Army to have to fight a peer adversary - a euphemism for Russia - in eastern Europe in the next few years, whilst our soldiers would undoubtedly remain amongst the finest in the world, they would, disgracefully, be forced to go into battle in a combination of obsolescent or even obsolete armoured vehicles, most of them at least 30 years old or more, with poor mechanical reliability, very heavily outgunned by more modern missile and artillery systems and chronically lacking in adequate air defence.".......