Normally on a Hotpoint the filters are located directly below the drum drainange point, inside the machine. They make 'em this way so you have to call someone out to do it, but it's quite easy.
Firstly, disconnect from the supply, and get good access to the back of the machine. There should be a small removable panel at the bottom - remove this first.
OK - you should see the main drainange pipe from the drum, and an outlet hose sheathed over it and held in place by a metal ring. This is the large ring we're talking about - not the smaller one that connects around by the pump.
Remove the ring - you may need a bit of muscle here - taking care not to break the rubber hose.
Inside the hose you will find the filter. It's a small piece of cylindrical plastic with holes. You can take it out to give it a clean, but also check the hose and give that a wipe out too.
If the machine is a couple of years old (like mine) you may find a few quid stuck in the filter! Replace everything the same way, ENSURING THAT THE HOSE IS BACK ON GOOD AND TIGHT!
Hope this helps.
Lieutenant Columbo, August 2006