I have just taken off the yellow on/off switch and followed the hints above. Excellent, however I found that by simply moving the flexible hose out of the way, you will see a small hole that leads from the hose housing into the on/off switch assembly. Just push a small screwdriver through the hole as that pushes the plastic clip away from the assembly and the on/off switch just lifts off.
Dyson deny there is any problem with the wiring where it goes into the switch, but this was the third time it shorted out. Dyson of course refuse to assist in helping to remove the switch (elf and safety, blah blah) but we know better. In fact, the design is so poor when wires are twisted or pulled (everybody does it for Heaven's sake) there will eventually be a short which could kill someone. They make 35 quid a visit too!.
Bryan, May 2009