As has been said there is little difference between using an Irish or a British passport. The only slight difference, which makes no difference on entry, is that British citizens have a right of abode whereas Irish citizens have a right of residence. Practically speaking this is of little consequence - it’s slightly easier to remove a right of residence than it is for a right of abode.

And obviously, just to clarify, whilst you can indeed enter without a U.K. passport but try to prove it through other documentation, I don’t recommend it if you’re looking to expedite your entry!!