Just entered UK last week. The immigration form is scanned with your phone from the sign at the beginnning of the que. You then open the program and fill in the details. Not easy if you don't have a working sim as the free wifi cuts you off before you can complete the form unless you are really fast. You need handy, your ticket for flight and seat number, a contact number, an email address, the address where you will quarantine for the next 14 days. There was a queue of us incompetent old folk that needed help. After a long flight it a mind bender. There is help at immigration to fill in the information.