United attacks American Airlines today with low fares to Paris and London from Dallas, Miami and Philadelphia. Miami only has London on sale. These fares are in the $400s and $500s from mid-September to April 2017. Lowest fares are Air Canada flights with United flights from $1 to $50 more.
$533 Dallas DFW – London LHR (Sep-Oct lowest dates; $574 more common).
$489 PHL – Manchester MAN United (Amtrak to Philadelphia to EWR)
American Airlines Philadelphia PHL – London LCY