Originally Posted by
travellingtechie
Last time I transited through Heathrow from domestic to international I still had to go through security so they don't even trust other UK airports now!!
The details of your transit matter.
If you went through security you must have changed terminals
Certainly arriving into T5 there is no security from domestic into the departures area. Though I'm not sure about T2- the only other LHR terminal with UK domestic flights.