Originally Posted by
anabolism
Sorry, I'm confused. If you arrive on an international flight, there shouldn't ever be a way to get land-side without clearing immigration and customs. In LHR, you can get off the plane and immediately clear both and go land-side, or you can use FCC to get, say, from T5 to T3, and then choose to clear immigration and customs and go land-side at T3.
What I meant was that you may go through the hassle of clearing FCC, only to realize you want to do something land-side and then have to deal with immigration. In the US you automatically go through immigration first so you then pass between air-side and land-side as you wish.