Europe’s biggest budget airline is selling flights from the UK to Greece for under £15 – representing a cost of just one penny per mile – even for imminent departures.

Fares on other Ryanair flights, between the UK and Italy, are as low as £4.99, signalling a bitter autumn fares war.

As the peak summer month of August ends, airlines are desperate to entice passengers on board at almost any price. Normally fares very close to departure are sold at high prices.

Ryanair, which has long had a policy of cutting fares to whatever level is necessary to fill planes, is taking on rivals such as British Airways and easyJet with tickets that cost less than the train to the airport.

Tomorrow’s 9.15am departure from London Stansted to Athens is priced at just £14.99, for a point-to-point journey of 1,500 miles.

The fare is undoubtedly a loss leader, since the carrier must pay Air Passenger Duty (APD) of £13 – plus a handling fee for each traveller passing through the Essex airport.

Ryanair will hope to boost the fare by “upselling” extras such as a seat assignment (minimum £8) and priority boarding plus an extra cabin bag (£16, more than doubling the basic fare).

The cheapest British Airways fare from London Heathrow to Athens on 1 September is £85, which includes two cabin bags weighing a total of 46kg; easyJet’s flight from London Gatwick is priced at £68.

Other Ryanair deals – which are not part of any short-term seat sale  – include £4.99 from Belfast City to Milan Bergamo on Saturday 4 September, for a distance of over 900 miles.. Later this month, the carrier is set to abandon the Northern Ireland capital’s close-in airport.

Tickets to Alicante on Spain’s Costa Blanca for 1 September are available for £12.99, a penny less than APD, from a range of UK airports including Birmingham and Bristol.

Michael O’Leary, chief executive of the Ryanair Group, is expected later today to issue an optimistic forecast of the coming months – flying more than 10 million passengers in September, October and November.

But the airline boss is likely to launch a stinging attack on the UK government’s travel restrictions.

Testing to return to the UK – required both before and after a flight –  typically costs each passenger £100 in addition to the air fare.