Seattle and Denver are being added to Norwegian’s low-fare transatlantic network from Gatwick.

Fares have gone on sale at a lead in of £199 one-way for both routes which start in September.

Both will operate year-round with Europe’s third largest budget carrier challenging Virgin Atlantic’s newly launched Seattle service from Heathrow with more than 125,000 seats going on sale.

Norwegian will be the only airline offering flights to Denver from Gatwick, competing with British Airways’ service from Heathrow.

The Seattle flights will operate four times a week from September 17 while Denver will be served twice a week from September 16 by 344-capacity Boeing 787 Dreamliners. Denver will gain a third weekly service in the winter.

Premium fares on the two new routes at £599.90 each way.

The airline’s chief commercial officer, Thomas Ramdahl, said: “Our new Seattle and Denver routes reflect the huge consumer demand on both sides of the Atlantic for quality affordable long-haul travel.

“With our USA flights over 90% full, we are excited to add Seattle to our growing list of US destinations while breaking the monopoly on UK flights to Denver.

“As we expand our high quality services to the USA, we will continue offering passengers greater choice, convenient schedules and affordable fares when flying Norwegian.

“Our global expansion is also creating jobs in the air and on the ground in Europe and the US.”

Gatwick chief commercial officer, Guy Stephenson, added: “I’m delighted that Gatwick’s extensive 50-plus long haul route network will soon include Denver and Seattle, both top destinations for leisure and business travellers.

“Crucially, both cities are prominent business centres known for their hi-tech and advanced manufacturing industries.

“Both are also gateways for trade across the US so this new connectivity comes at an important time for UK businesses, including those that export cargo.”