It was going so well..
I took the back off and eventually got the belt around the drum and refitted all the rear seals etc. I then disassembled the front fan (slightly splitting the spindle but it seems to hold together) and threaded the belt around the spindle and pulley and reassembled.
My only outstanding issue is the microswitch for the water drawer. The lever has become detached from the microswitch and I can't for the life of me work out which way it is meant to go!