Bath tap won't switch off

[redwin11]

The toilet was flushed in our bathroom and suddenly hot water came out of the bath tap, which isn't even switched on!

I can't switch it off, although when we flush the toilet, it subsides, before starting again.

Any thoughts?!

 

[breezer]

washer has gone / going

when the loo is flushed the water pressure drops to other taps etc

 

[redwin11]

Ok, appreciated!