By definition an instantaneous electric shower should be on its own
circuit.
The implication of your (somewhat short!) posting is (AFAICS) that
the
shower is on the ring main feeding the tumble dryer. If this is so,
things
aren't fine at all. We need more information about how the two things
are
wired in.

hello. the tumble dryer is plugged into a socket.

the shower was wired in by my friend martin because he knows about
electrics. all i can say is that the cable goes through the bathroom
wall, round the skirting board in the bedroom and into a socket.

ill ask martin tonight weather the shower is on the ring main feeding
the socket.

harry