Originally Posted by
jsloan
TWOV allows crossing the border. OP would need to present proof of onward travel and admissibility to the next destination to the UK immigration officer. It needn’t even need be a flight — a train ticket to Paris and a Schengen visa would qualify.
It doesn't apply to the OP but for the benefit of other people in a similar situation reading this, I think I should mention that it is often false (according to the UK Government website) that one can transit from air to train or ferry without a visa in the UK. Transit without a visa in the UK must (for many people) be air to air. See as an exemplar:
https://www.gov.uk/check-uk-visa/y/c...where_else/yes
(BTW, although the UK's website doesn't make this clear, the dots mean AND, not OR: all those things need to be true, not just one of them!) Having said that, I don't claim to be an expert on UK immigration law so if someone knows I'm wrong, feel free to correct this.
Related to the OP, I'll reinforce what others have written already. Based on my experience, OP should assume that he/she will be told at check-in by UA agents that he/she must have a UK transit visa. OP will have to try to persuade the UA agents (with eg. printouts of documentation) that OP can transit in the UK without a visa and the UA agents need to call their internal help line to confirm this is true. OP must hope the internal help line gives the agents the correct information and the UA agents allow OP to board. It is not a certainty that UA agents will permit OP to board the flight.