On 20/08/2019 10:24, John Rumm wrote:
I havent a clue but maybe because the tap lever was in a mid position
it meant both tap outlets were open, if I had had the tap lever
swivelled for hot only possibly it would not have happened.

Yup, if its a proper mixer tap, as many bathroom ones are[1] then that
will happen.

[1] Kitchen style ones usually have a pair of concentric spouts that
cause the water to be delivered separately and mix outside of the tap.

Yes makes sense when you think about it and guess who never thought it
through :-(