Would love your advice on connecting a new light to the existing wiring on our ceiling light please! It’s a lot more wiring than I’ve seen on other images. And certainly more connections than the Neutral, Live and Earth one on the new fitting.
Neutral's on the far left, Switched Live is on the far right, Earth is at the bottom
Looking at your ceiling rose and the mixture of old-UK and IEC color coding present there, we can tell from the combination of two blacks and a blue going into the far left block that it's the Neutral (Return) side of this ceiling rose. Given that we know the fixture can't be connected to the Always Live (because the switch works), that puts the Always Live in the center, with the blue wire connected to the Always Live being a hot feed down to the switch, which was wired using plain IEC-coded T&E (brown, blue, green/yellow), so you'll want to take that blue wire off the always hot block and sleeve it with a piece of brown or black tubing, then put it back where it came from. Finally, the Live wire on your new fixture goes to the Switched Live block on the far right, which has the brown wire from the switch loop and a yellow onward switched-live going into it.
The earth wire of the fixture, of course, joins with the rest of the earths at the bottom of your picture. Once that's done, you can button things up, turn the breaker back on, and enjoy your new light! P.S. you probably should have an electrician look at this wiring at some point, as that blue wire joining in with the earths is rather odd, to say the least.