how can British troops - which have no fighting experience
You clearly do not read the news much do you. Afghanistan, Iraq x 2, Kosovo. This is as well as the covert ops the UK has taken part in. As for the Ukraine having 1.5 yrs of experience, they have kept the Russians at bay partly because of the advice from NATO as well as experience on how to use the weapons donated.
There is nothing to be gained by training in Ukraine. This is just political points scoring by the Tories who are under immense political pressure from their own party. This is placing a target on the personnel who will be based in Ukraine. It also opens the UK to attacks without the backing of NATO behind it. NATO only applies when the country is attacked first.