On my cactus in london england. Should i get rid? Thanks!!

Hi J,
It's hard to know exactly what kind of caterpillar you have there because I can't really see both ends.... and I'm not so familiar with bugs in the U.K. But these 2 websites might be of help to you.

Oh, and don't panic! Most caterpillars are easy to deal with.
https://www.naturespot.org.uk/...
https://www.rhs.org.uk/biodive...

The picture's a bit fuzzy, but if it's brown, it might be a stone centipede. They're carnivores that won't bother your plants but eat other bugs such as fungus gnat larva and sympylans.
If it's white, it's more likely a sympylan. They eat plants, roots, seeds, sprouts etc. So, they're undesirables in houseplant pots, and can be pests in greenhouses and agricultural land. I don't know how to get rid of them.
https://extension.usu.edu/vege...
There can be an amazing amount of life in soil--good, bad and ugly-- even in potted plants.

I was thinking as Ms Doe- some soil crittter. I'd remove it because I don't expect potted indoor plants to have a complete and balanced soil community, and because while I love outside critters, inside ones are a bit creepy.