Any ideas on this toilet flush?

[PeachPotato]

Sorry for terrible pictures!

Toilet flush is leaking (water flowing into pan once cistern full). Does anyone have any ideas which flush available from somewhere like screw fix would be the replacement? Can I fit it myself?

Try twisting the body. I've had this numerous times. It may take 2 or 500 times to get right.

Mine periodically is just like this, mostly just a random bit of limescale stopping the mechanism temporarily, usually resolves by hand wiping to dislodge any crusty bits?