Not sure myself laney but there's a site called Uk Safari which identifies caterpillars so you might get it on there if no one here can help. If nutcutlet's on here today she will probably know
ty. will have a look. x
At the risk of nut telling me I'm completely wrong, I'm going to say that it's a Grey Dagger moth caterpillar. They live on birch, hawthorn, apple and plum leaves.
Ty waterbutts. x