A BIG Thanks to all that answered.
In the end - I took the washers out of the old tap (was still knocking around the garage) and they worked perfectly.
They were much thicker than the ones supplied and were also clear in colour, so suspect they were made out of a different type of rubber...
Dear all.
I've recently taken an very old mira bar shower that I have replaced with a Iflo Richmond Thermostatic Bar Shower which is now leaking at the brass unions that were supplied (I took the old ones out).
The instructions specifically say not to use PTFE tape on the unions (the old...