I just read this on the Home Office IRIS registration website:
If you are in Heathrow Terminal 4:
Follow the signs to gates 1 to 6 and the enrolment room is between gates 3 and 4.
This enrolment room will normally be open between 07:30 to 19:30 hours
Unfortunately there may be on occasion the need to close enrolment rooms at short notice for operational reasons. Such closures will be kept to a minimum and will be as short as possible.
Due to a technical problem, the enrolment room will be closed until further notice.
We apologise for any inconvenience caused.
Grrr..!




Can I sign up at a different terminal to use the T4 IRIS?
Cheers
/MHL