Originally Posted by
gpb_croppers63
You almost certainly will not be able to go through security in T2. I had an EI flight out of T1 a couple of days after T2 opened and tried to go through security there. I was told in no uncertain terms that I wasn't allowed to do it. I was first lied to and told "there's no way to walk airside between T2 and T1" and the lady only changed her tune to "no, it's just not allowed" when I told her that a friend of mine had done exactly what I was trying to do just the day before. She was not budging and I didn't have that much time so I just gave up at that point although I did complain to a Heathrow employee in a purple coat about being lied to. She was very friendly but basically told me that security are a law unto themselves.
In your case you may be glad she blocked you. I'm not sure they would have been able to take your photo and enter you into the biometric system at T2 since there are no domestic flights there currently. As a result you would have gotten to the UK/IE biometric check and been turned back. This happens to someone every few days and it's a tremendous hassle.
The whole system is nuts. If it was like any other airport you would have a domestic section and an international section and you would only need the biometric kerfuffle if you wanted to walk between them. It would be impossible to accidentally end up on the wrong side without having passed through the check.