Ryanair is offering one million seats from Britain to European destinations for as little as £16.99 from September 22 to December 16.

Tickets have to be bought over the next 12 days.

"We're doing this deal now to re-emphasise Ryanair's position as Europe's leading low fares carrier," said Ryanair's chief executive Michael O'Leary said after raising a promotional banner outside a BA flight shop in central London.

The offer is a response to British Airways' own weekend seat sale in August and to the launch earlier this year of BA's own discount airline, Go.

BA sold around 2m tickets to 80 destinations worldwide on its discount weekend.

"British Airways ran what we think was a fairly limp seat sale two weekends ago and we want to show BA how a seat sale should be run," countered Mr o'Leary.

On Tuesday Ryanair announced that it carried a record half a million passengers in August, 25% up on last year's figure.

In May British Airways created its own low budget European airline Go to compete directly with Ryanair and others.

"Long-term, all the budget airlines won't all be able to stay in the market but Ryanair will, with perhaps one other but there isn't room for all of us," said Mr O'Leary.

In July the number of people flying from Britain's seven major airports rose to 11.2m - 9.2% above last July's total.

Ryanair's discount fares (one way, tax not included)

• £16.99
  From London Standsted to Prestwick in Scotland, Rimini in Italy, Kristianstad in Sweden, or St Etienne in France. Also from Luton and Liverpool to Dublin.
• £19.99
  From all regional airports to Dublin
• £29.99
  From London Standsed to Pisa in Italy, Stockholm in Sweden, Carcassonne in France and Oslo, Norway.