Something for people planning to cycle to/from Heathrow terminals 1,2,3 to keep an eye on.
According to this web page http://www.heathrowairport.com/commuter/commuting-to-heathrow/by-bicycle (which is for Heathrow workers, not passengers), at some unspecified point in the future both side tunnels (which are the ones used by cyclists) will be closed at the same time for refurbishment, no mention of dates and duration. The same page implies there is no safe cycle access to T1. Alternative provision for Heathrow workers is a cycle hub to the north and come in by bus.
The web page for passengers http://www.heathrowairport.com/transport-and-directions/cycling-to-heathrow mentions none of this. I'm assuming the alternative for cycling passengers is Heathrow Express to/from T5, from where the cycle routes are good, but this is just my guess.
I discovered this after arriving back at T3 late in the evening. By the time I'd reassembled my bike (tandem actually) it was gone 10pm. A random airport worker I asked for directions to the cycling tunnel told me how to get there, and then said he thought it was closed. It is open at present, and once you've got to it, it's fine. What is normally just the outbound (western) service tunnel is cyclists only for both in and outbound.