In message , at 10:28:54 on Fri, 30 Dec
2011, tim.... remarked:
but why will the majority changing flight go land side in the first
place

How else do they change terminal?

By taking the airside transfer buses and using the infamous "Connections
Centre" to be re-screened.

Much fun for all the family at this stupidly long url:

http://www.heathrowairport.com/heath...-guide/flight-
connections/connection-guides/international-arrival/international-
departure

Where (eg) T4-T5 is timed at 105 minutes. No wonder some people think
going landside will be quicker.

But that includes 30-45 minutes for queuing up for security/waiting in the
far lounge

You'd have to allow this time if you went on the tube.

The actual transfer time, including waiting for the bus is going to be 30
minutes or less. I doubt that you will better this going land-side and back

As I've tried this, perhaps you'll allow me to disagree? I even had a
"race" with a colleague from T4 to T1, he went airside and I went
landside (on HEx) and won.

Part of the problem is the accessibility of the airside bus, which at T4
goes from the very SW corner of the terminal whereas the immigration/
customs exit is in the middle of the building. If you land at one of the
gates at the NE of the building the bus is about 20 minutes walk away.

Although the geography's slightly different, I also lost a "race" at
Charles de Gaulle between landing long haul and getting to the Air
France departure lounge for the hop to the UK. I went airside on the
bus, and they went landside on foot.

--
Roland Perry