Update on this!
Got a replacement bulb holder from Homebase, with the intention of swapping the whole thing over, but was thwarted as the remaining part of the old one wouldn't give up it's grip on the base. However, although the old one was a push fit and the new one a screw fit, it actually gripped pretty well with a mix'n'match set up.
This was until yesterday, when I came to switch it on, with the push/push switch just below the bulb, and the damn thing blew up almost in my face!

Glass everywhere, and an ever so slightly cut right ear, which apparently stayed bright red for the rest of the evening!
To be fair, I'm 100% certain that this wasn't down to a bad holder or bad workmanship on my part. The fit was very snug, and examining the wiring afterwards, it was still securely in place and, unlike the first time which led to the replacement, there was no sign at all of any burning/scorching. I'm sure that it was simply a dodgy bulb, but nevertheless, scary!