I was thionking of English, Welsh, Scots Gaelic, Irish (don't forget that "and Northern Ireland" bit in the title of the union)and Shelta (which is not as common as it used to be, but is still heard in Scotland, in Northern Ireland, and in parts of England and Wales, as well as in the Irish Republic - it seems to have originated as a sort of GA-GD-EN creole, borrowed some (very few) words from Rromani, and undergone deliberate obfuscation to allow secrets to be discussed where gadzhe could hear, and is now rapidly becoming anglicised - more so in Ireland than in England) so I guess I should have said 6 as had missed out Scots which is certainly both indigenous and alive. Some people would say that Rromani should be counted too, as it's been in the territory which is currently the UK since well before the union of crowns in 1605, but I left it out as it's not really indigenous. Some would want to add Cornish, but I'm not sure the revival is real. Manx (which isn't in my count, because Ellan Vannin is not part of the UK) rose from the almost dead - it even got a new orthography invented for it because no native speaker was literate in it and the Bishop who promoted the reviaval hadn't the wit to ask people across the straight in Scotland if they knew it, which explains why it's so horribly difficult for speakers of the other Goidelic languages to read it - but I'm not convinced that Cornish will manage to do the same rsurrection act so I kind of sit on the fence about Cornish.