Well I guess it was too simple but I have seen posts from a number of other people who have had the same problem ... where do you start? But no-one has answered their question. So I will answer it myself:D

At the back of the top there are two plastic catches - the outer ones are not catches but the inner ones are. Poke a flat screwdriver in the slot and this will raise the catch slightly so that the ridge clears the slot and it is enough to be able to ease the top backwards on each side.

Then the whole thing comes off by pushing the top backwards.

The rest is a doddle - just rather messy and the fat was smelly too.:D Yuk.

Why don't DW manufacturers include waste disposal technology? Instead of telling folk to rinse their stuff, just bolt on another goody and accept that most of us - even those who should know better - just sling the plates and saucepans into the DW and press the button. And after the final rinse, a super slug of degreaser could be directed around the pipework but not at the plates.

This shouldn't be too difficult...

Hey they could charge more too!