Have taken washer off dripping tap handle, what’s the bit I need to replace? (photos!)

[DollyDoyle]

We worked out that the kitchen mixer tap has been dripping due to the right hand cold tap.

We’ve got this far. What do we need to do next please?!

That all comes as one part. It's called a tap cartridge. Take it into screwfix and they'll match it up for you.

What @alittleworriedlamb says.

Ah ok so it’s not just the little black rubber ring that we need to replace?

So glad I posted!