They've put TRVs on all the rads bar one and have ripped out the
old room thermostat. Is this normal?

There must be some sort of boiler interlock installed. Otherwise, the system
does not comply with the building regulations. The interlock is normally of
the form of a room thermostat. However, it is permissible to use TRVs and a
flow switch to detect that all the TRVs have closed off. You need to find
out if your system has such a switch. If it does not, get the installer back
and ask how the boiler interlock requirement of Part L1 is met.

Actually, thinking about it, it can't be compliant, as the bathroom radiator
without the TRV would mean that any such flow switch would be ineffective.

Christian.