Here are the holidays for May where immigration offices around the country will be closed.
Thursday 4th May - Coronation day.
Friday 5th May - special “bridge” holiday.
Wednesday 17th May - Royal Ploughing Ceremony
(Awaiting confirmation if the 17th is a regional holiday or nationwide. Will amend as I get confirmation).
If you can possibly help it avoid going to your immigration office on the days surrounding closures. They tend to be way busier.
Note. May 1st is Labour Day but immigration offices are open.
Also note that immigration booths at all air or land borders are open as usual.