There are some great deals from San Francisco SFO and San Jose SJC to London under $500 round trip with all three alliances.
Flight departures are March to May 2017.
British Airways has SFO to Jersey JER in low $400s. Jersey is a UK island off the coast of France.
United Airlines San Francisco SFO – London LHR – SFO nonstop
British Airways San Francisco SFO – London LHR / London LGW (ground transfer) – Jersey JER – LGW / LHR (ground transfer) – SFO