Originally Posted by
mmxbreaks
Above has inspired below
OP, in the instance you can get a direct (I don't know if you can), then it'd be potentially beneficial to go direct into London, then get the Eurostar train into Paris Central to cut back on the flights. Just a thought. This may also cost more, thinking about it, but worth investigating in my opinion.
I would not recommend that at all. You'd have to enter the UK, which can involve very long lines. Then the LHR=>St. Pancras is a total hassle. An airside transfer at any UA hub would be
much easier.