last time I was at LHR, they had a slew of Intra-european flights landing at once, and since most of the flights are international into that airport, they went through passport control. They allowed citizens from the EU, EEC, some other organization, and Swiss citizens to go through the line, all they had to do is show their picture page of the passport and they were waved through, nothing was formally checked.
I (Swiss) was lucky last time at LHR too and just waived through!