The black cap you see is the filter.
It should be attached to the white cap but appears to have been pulled or broken off.
Try levering it out with a couple of screwdrivers (water will pour out if it comes out, if there's water in the machine).
If it won't come out, you'll need to strip the drain pump/filter chamber assembly out of the machine to get it cleaned out.
When you try levering it, ensure you don't damage the part the outer cap screws into and seals onto.
Check it out, see how you get on and get back to me if you need more help.
Hope this helps
Thanks for the reply-had a quick look this evening but filter seems well and truly stuck! Will have a better look over the weekend and get back to you.
Thanks a lot
Looks like you need to strip the pump / filter assembly out to get this sorted out.
You may even need a new filter housing and filter.
My partner has cleared the pump and all pipework of horrible gunk and machine is now working again. The black part of the filter appears to be glued into the machine so we do not think it is removable? Not sure what we can do about this to stop it happening again without a filter to clean?