Budman:

There's no such thing as an "international" terminal at Heathrow - or rather, they all are, except for a couple of gates tucked away at T1 where they have a domestic flight about once a week.

Since the EU has no common system for border control, it's irrelevant whether you're going on to a destination in another EU country or in Outer Mongolia.

Niblette is correct. If you already have BA boarding cards, you arrive at T3. You get a bus, airside, from T3 to the Flight Connection Centre where you go through security. You then walk the passageways to the relevant T1 gate - which may be next door to a BA flight for San Francisco or an SAA flight to Jo'burg.

You go through immigration at Munich, and your bags are liable to be stopped by Customs there - though Customs inspections of bags arriving from outside the EU are about as rare as domestic flights from Heathrow. Hens' teeth, by comparison, are a drug on the market.

Budman:

For further clarification.

You DON'T go through immigration at Heathrow, unless your bags have to be collected there.

You're unlikely to have time for a pint - but it wouldn't be good for you that early in the morning anyway.

There's often queues for the inter-terminal buses, security queues at the FCC can be heroic, and BA are pretty anal about wanting you at the gate on time. It also all adds up to some pretty revitalising walking.

But, in the unlikely event you do have 5 mins to spare, there is a Wetherspoons airside at T1, it does include drinkable beer in its range as well as the fizzy muck they serve in your native country - and it opens at 0530.