If any of you are wondering how to navigate a transit fro. The US through LHR and on to Switzerland, requirements, forms, etc. there are several helpful threads for this now on the Switzerland forum.
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Seattle, WA
16254 posts
This one has a link to the form itself, and lots of discussion about your "departure country":
Quick answer: if you stay airside at Heathrow while transiting from your US-origin flight to your Swiss-bound flight, your departure country is the USA).
This thread discusses how to enter your phone number on the form in acceptable format: