Well, interesting - the relay box shown in the YT video is not there on my UK Jazz! I was initially disappointed but looking around under the bonnet I found it on the opposite side under the filler neck of the washer bottle, bingo!
Slightly tricky to remove the box lid but managed it and extracted the relay at the front of the box. There are three relays, two side by side and one by itself at right angles to the pair - that's the one I believe operates the AC magnetic clutch.
Using another YT video I have tested it with a 12v supply and believe it has failed. You need to be careful - applying 12v across the brass coloured terminals still caused an audible "click", but with power on you need to check with a multimeter for continuity across the other pair of terminals (copper coloured). There should be continuity, but on mine, power on, it's open circuit.
So, have ordered a new relay, and keep my fingers crossed!