As a Brit, I would say never. I'm not sure how I would feel if nukes were used on Britain, but I've always imagined nukes to be anti-progressive. 

"Lets defeat the enemy and take all their stuff!" 

Nukes.

"Yay we won! What did we win?...Nothing!"

The problem for Russia is that all it wants from Europe is threatened more by the use of nukes than conventional warfare.