My ariston AWD 12 won't do fast spin?

Hi,
I've got a 3 yr old Ariston AWD 12 (UK). Recently the washing has started to come out very wet. (I don't use the dryer cycle)When I watched the spin cycle it starts to spin then cuts back on the speed, then repeats. It never accelerates to the full spin speed. It's just like when the load is out of balance, when it'll slow down to redistribute the load and try again. This happens every time regardless of load. I can hear the drain pump running throughout the cycle and the water drains away normally after rinsing.

I've had a look inside the case and the drum suspension mounts all look normal and secure and the drum can move freely on its mountings. No, I haven't left the 'transit' screws in! I can't see any obvious loose wires or connnections.

Any ideas??