You probably need a new wiper motor "park-swich" Fitzy.

It's the little white plastic unit situated behind the wiper-motor and
it has a few coloured wires connected to it.  It's simply a case of
removing the old one and refitting a replacment, whilst ensuring the
wires are refitted in the correct order.

It's worth replacing it soon, because i've found that a faulty
park-switch can cause other electrical faults, such as blowing fuses or
misreading gauges etc.

Taffy