I just noticed that, on Monday, Lidl UK are offering an adaptor to allow the use of their accessories with other makes of pressure washer.
I seem to remember that lack of inter-connectability has been an issue for quite a few people. It does not expressly state Kärcher, Nilfisk, Bosch or any other make - so make sure before purchase! I don't know and, at present, don't need to know, having what I need as a Nilfisk kit.