Changing light fixture with red/black UK wiring using only black wires

I am planning to change a ceiling light fixture in my 1980s-built home in the UK.

I had a look at the box and was surprised to see 3 red wires nutted (?) together and 3 black wires feeding the light. And a healthy amount of tape.

Even though the wires are red and black, the fact that the 3 red wires sit unused does not seem to match any UK wiring scheme of any era, but hopefully I am wrong!

The two beige cables go to the light box hanging below.

Can someone tell me what's what? Note again this is in the UK. I don't know how old the wiring is but the house was built in the 1980s.