Even very late emergents such as some individuals of Common Ash (Fraxinus exelsior) would normally be coming out now so I am guessing that your tree is dead? Cotinus and some legumes such as Cercis and some Sophora's are also late but would normally show something by now, especially in relatively mild Northern Ireland.

Would help to know what it is though.

can you try scratching under the bark to see if theres any sign of life ? if it is dead it my be worth finding out what killed it .