Warts On Dogs Tail By Butt I've Just Found A Wart Like Growth On My Dogs Tail?

I've just found a wart like growth on my dogs tail? - warts on dogs tail by butt

He went out, and it seems as if something hidden beneath the skin - there was no bleeding or anything, and seemed in pain with him. Has anyone any idea what could be? She goes into the woods a lot, because we live in the country. I live in the UK if it helps.