You could well be right about the fuse blowing as after consulting my manual it shows a picture of wipers and washers covered by 1 fuse.
In the panel to the right of the steering wheel there should be 3 rows of 5 fuses. There are 4 fuses slightly offset from the 3 rows, ignore those. The wiper/washer fuse is on the right hand side in the middle row on the end. The manual shows it as a 20A. The manual is for a left hand drive so it says that its to the left of the steering wheel, so I am assuming they have just moved the fuse control unit to the UK side rather than mirrored it. Does that make sense? There should also be a picture layout inside the fuse cover.
My 156 is a 2001 so hopefully your fuse layout is the same.