since all i can see at least is the fungi NOT the tree that's it's growing on any i.d. of the tree you're interested in must (for me at least) wait on receiving more pictures of the tree itself. BTW, some fungi are very host specific but others can grow in a number of different types of tree so knowing the i.d. of the fungi itself (i don't, LOL) is not a guarantee for knowing the tree it is growing on.

Barry, these types of bracket fungi grow on many different types of trees. We would need to see more of the tree itself (leaves, any seeds or fruit, overall shape) to confirm an ID.

Generally, these types of fungi are symptomatic of heartwood decay or rot so do not spell good news for the health of the host tree.

OP is in UK which cuts down the possibilities - but still a lot to choose from. More pictures are needed. Assuming it's in woodland rather than a garden it shouldn't be too hard once we have more info.