With currently released British Airways promotional you can vsit the capital of the United States of America as well as Svandinavia (Oslo, Copenhagen, Gothenburg, Stockholm) or Dublin on your ways. Based on service of this Oneworld airline you can book cheap open-jaw flights from Scandinavia or Ireland to Washington and returning back to London (non-stop service) already for £229 (€265). Remember that you can not skip first leg of your outbound flight between Scandinavia and London…rest of your itinerary would be cancelled..This offer is good alternative if you want to plan 2 in 1 trip as above cities are well connected by many low-cost airlines.
British Airways promo sale is available when departing from Europe to Washington from 1st of October and 18th of December 2018. (The earlines inbound date from USA to the UK has to be on 298th of October and latest on 31st of December). Max stay 3 months. You can book your hotel in Washington via Booking.com or Hotels.com.
Booking sample of British Airways promotion offering cheap open-jaw flights to Washington return to London from £229 (€265)! You would depart from Oslo to Washington on Sunday, 11th of November and return on a non-stop service from America back to London on 25th of November 2018.