Vapourer moth larvae. You can try spraying, but that's not easy with a whole tree. Usual remedy is to pick them off and squish 'em, but again, difficult with a large tree.

Don't, they're lovely

I agree with Worthy - good to protect 'em. Are they doing real harm to the tree? You don't say what tree it is and hard to tell from the pic ( for me anyway).

I can't remember what type of tree it is but it's only small and is in a pot. Would prefer not to kill them but they are causing a lot of damage, not sure if the tree will out last them! How long will they stay?

The vapourer is considered by some to be a serious pest, and it's caterpillars can do a lot of damage when in large numbers. They eat the leaves of almost any deciduous tree, so put them somewhere in a hedge (perhaps not your neighbour's!) where they'll pupate shortly. Wear those elegant gloves, as the hairs of some of these can cause irritation or worse.

Thank you for your replies. I had another look this morning and there seem to be less of them so perhaps the birds are helping out!
I'll go out and remove the rest later on.

Good luck with the removal Reem :)

ive found one on one of my roses today,how it got there i dont know and as far as i know i dont think its munching on them. ;-)