"Aug 23 2016 Update
I hesitate to offer advice, because I am not a lawyer. But I’m seeing a lot of stupid conversations and bad advice spinning out from this. So I will say the following.
Speakers: Do not lie at a country’s border and say you are going on vacation like some people are suggesting. This is both unprofessional and illegal. Also, do not take a conference at their word that “there shouldn’t be a problem.” Reading the docs on a government site and some online travel discussions is not adequate preparation. The organizers should have enlisted the services of an immigrations lawyer. It is not overkill if a lack of due diligence lands you in this situation.
Conference organizers the world over: Seek the council of an immigrations lawyer before inviting speakers from abroad. Don’t just look up stuff on the Internet or listen to your friend who’s “been doing this forever and never had a problem.” You’re responsible for someone’s well-being and possibly their livelihood and/or career.
As for me: I’ve largely moved on from this and have accepted that I will not be going back to the UK. This post remains to chronicle what the deportation process is like at Heathrow and its lasting effects. The post has raised awareness among speakers and organizers about borders and visas, and in the general public, it raised awareness about the consequences of border policies and has got people sharing their own stories. This is good. Please continue.
Per Bjesse, Koen Claessen, Mary Sheeran, and Satnam Singh. 1998. Lava: hardware design in Haskell. In Proceedings of the third ACM SIGPLAN international conference on Functional programming (ICFP '98). ACM, New York, NY, USA, 174-184. DOI=http://dx.doi.org/10.1145/289423.289440"