Originally Posted by
ringingup
This is surprising, as it contradicts the advice that has been given here several times.
And I've been trying to correct this in a number of posts (and have vaguely given up!). Visiting T5 is different, but if visiting T3 you do not need a T3 boarding pass to enter airside, if on an international connection (and DUB counts as international in this context). So long as you go airside to T3 directly after arrival into any LHR terminal, then you don't need a boarding pass. You will be asked for a boarding pass at security in T3, but it's ok to say "I'm going to the lounges/shops/whatever". Now there are a number of reports that the
oneworld lounges in T3 don't care which terminal you use (the staff may not be aware themselves of the myriad options), nevertheless in theory you could be denied admission to these lounges. You would be OK for the paid-for lounges however. Personally I wouldn't bother due to the hassle and the potential risk of being denied lounge access but at least on paper it can be done.
HAL put up signs at Flight Connections advertising the facilities in the other terminals.