That circlip just stops the spindle dropping down inside the cartridge, you would only want to remove it if you wanted to dismantle the cartridge itself, but you would still need to unbolt the cartridge first and pull off the blue bit, as the insides remove from the bottom. Turn the water off, support the tap and unbolt the cartridge, and as Bobster-cyw said, once you've identified the cartridge just bolt it back in until you can get a replacement.
I just repaired mine last week, exactly the same problem. Turn your water off and remove the cartridge with a spanner. I then found a matching one on eBay (just match up the measurements) and pop it back in. No more leaks (y) I wouldn’t bother with removing the circlip, just the whole cartridge. Mine was about £7 Obviously once you’ve ordered just pop the old cartridge back in for now so you can continue to use the tap.
Being a "spanner| is not a compliment.
Thanks for everyone’s input overnight. I don’t think it’s the ceramic discs that have failed as the tap isn’t actually dripping, the tear drop leak is where the circlip is. It’s not constant - only when the lever is pulled. I’m not that confident when dealing with water and as @spannerzone says, the last thing I want is a dismantled tap that’s out of use for a few days. I think the best thing to do would be to remove the circlip and see if I can pull the blue spindle bit out and see if there is a perished washer on that. I’m not sure the circlip is holding anything actually in place,(as it spins round freely (the same on the hot tap))more to stop the spindle from sinking downward (confused)
If it is leaking around the spindle, then it might just need a rubber 'O' ring to replace one on the spindle and a drop of silicone grease to lubricate it, if the OP can get the cartridge apart without breaking the ceramic parts. If the OP is in luck a generic cartridge might fit screwfix have a small selection starting around five quid. https://www.screwfix.com/c/bathrooms-kitchens/reviver-kits-tap-spares/cat820108?producttype=ceramic_tap_glands|ceramic_tap_cartridge|tap_valves|threaded_tap_glands&cm_sp=managedredirect-_-plumbing-_-tapcartridge