Full Valid Passport
Ensure you have a full Passport as you enter the UK likely with at least minimum six months still valid. Any EU country ID cards are expected not acceptable to UK Border control.
If you are given a dated Entrance stamp on entry into your passport make sure you receive a dated Exit stamp on departing into your passport. This is part of the in/out Schengen Zone coupled with 90 days permitted visit so you are shown not over staying due dated Exit stamp.
We suggest first checking these websites before committing to your travel.
Travelling to the UK from Ireland, Isle of Man, Guernsey or Jersey