Los Angeles to London nonstop flights are available for around $550 round trip on all three major alliance airlines today for departures from early December to early May. There are even dates around Christmas holidays with United Airlines.
Google Flights fare calendar shows every date available from early January to May 11 and nonstop flights are available most dates.
Virgin Atlantic nonstop flights are bookable as Delta or Virgin. American and British Airways both offer nonstops and some itineraries use Aer Lingus for London –Dublin one-stop segments.
United Airlines Los Angeles LAX – London LHR nonstop flights
$565.86 round trip Mon Dec 19 – Tue Dec 27