But the UK wouldn't get any support from the West if Russia were to invade, so would have to deal with Russia alone, with our 'pitiful' military?
We are part of NATO. Our military is part of NATO. Pretending we are a standalone nation with a standalone military force is deliberately misleading.
Ukraine isn't part of NATO, yet has had 'defense' support from the West which has stopped Russia in its tracks. Russia thought it could breeze in to Ukraine, take control of Kiev and move on with life. They didn't, they were stopped embarrasingly short - way before defense support was supplied by the West.