the incursion into Kursk was a test to see how Russia would respond and where that red line was. Now, the test was the destruction of nuclear bombers - to see how Russia would respond. This is pure poking the bear to see what the reaction would be.
The UK has always been behind and pushing this war with Russia, and again there are whispers of their involvement in this bombing of the Tu Bombers.
Russia has every right to defend itself, and now, since it's nuclear arsenal has been attacked, they have a right to respond in kind with nuclear weapons.