but UK experts say they could pose unique fire safety challenges.

Depends on implementation. We already have Lion cars with batteries that can be genuinely dangerous.

Trains are large enough that moving to LifePo4 is very practical.

These do not have the self ignite and supporting risk of other li tech. They are much safer than lead acid bats.

But even with lion. I feel safer with regulated train companies staff, then personal car owners maintaining them.