I thought I'd let you know what's happening.... I went to Electronic Partners
https://uk.electronic.partners/ as suggested, and they said they'd be able to fix the connector - fantastic. I posted off the earbud on Thursday, and they told me it was fixed on Friday, although too late to send out. Cost c£80 including a £30 priority fee. It then got lost in the mail coming back, and after phoning Royal Mail it turned up today (Monday) - a week after being posted 24 Tracked.
The earbud doesn't work properly. I've been playing around with different cables, players, and earbuds to try to isolate the problem but I can't make sense of it. I've ordered another cable to arrive this evening from Amazon and will see what happens. If I can't sort it out then I can send the earbud back to EP under warranty. I'll let you know.
EDIT: I ended up sending the earbud back under warranty. This time they fixed it properly, although it was annoying that they returned it 48hours - they ought to treat warranties as priority.
EDIT: It's now 3 months later and the connector is loose again. EP won't fix it under warranty as it's more than three months since the original fix, also it's less than three since the warranty fix. I won't use them again if I can avoid it.
I'm now trying fixmyheadphones here
https://www.fixmyheadphones.co.uk/ - at a cost of £75.
EDIT I got the earphones back fixed after 5 weeks and they work. It's been a couple of weeks or so now with no issues. I did have a bit of a bizarre interaction with the guy as when I inquired what was happening he told me a couple of times he'd be sending them but didn't, and ultimately accused me of whinging. All I'd asked for was an honest update. Anyhow fingers crossed they keep going now.
Nick