Hope he takes the advice given to call in an electrician.I do struggle with threads like this.
The OP is now going to fit this towel radiator, probably in a bathroom that may or may not have 30mA RCD protection. Maybe its in zone 1, maybe not.
It may or may not have a working earth (no Zs will be done), and there may or may not be existing IR faults on the circuit.
They may be using 3 core flex (0.75mm or less) and they may just tape up a choc block in the loft when they pinch power.
I think a little knowledge is dangerous and we should either take the time to fully explain all aspects of the job to the DIYer (which I very very occasionally do), or give no advice at all (which I usually choose).
Sorry, I know I'm going to ruffle feathers now, don't mean to!
As this is in special location he needs to adhere to the regs for this area most importantly as it will be an addition the said work that is.