San Francisco to London tickets for travel in May 2019 are as low as $420 nonstop with Delta Economy Light flying Virgin Atlantic and one stop Air France/KLM return. British Airways nonstop tickets are as low as $428 with one stop itineraries as low as $400 round trip.
Departure dates: May, then low fares return in mid-August to November 2019.
Delta Airlines Economy Light ticket
San Francisco – London LHR – Paris CDG – SFO
$419.83 round trip Mon May 13 – Wed May 22