The bitter battle between Britain's biggest airlines has taken another twist, with easyJet promising free tickets to business passengers whose flights are late – and taunting its rival, BA, into the bargain.

"A free flight if you're late. Or sweet BA?," is the slogan for an ad campaign the budget airline is about to launch. "If an easyJet flight arrival is delayed by more than 15 minutes, our business flexi passengers get a free leisure flight to anywhere on our European network. But if you'd prefer an apology over the tannoy and a bag of peanuts, we recommend our competitors."

The Luton-based airline is seeking to repair its reputation after a dismal summer in 2010, when it was plagued by cancellations and delays. It is also seeking to publicise its "flexi fares" – more expensive, flexible tickets that are designed to lure business travellers from other airlines, primarily BA. The result: an unprecedented short-term promotion that allows any passenger whose flight is delayed while travelling on a "flexi fare" in October or November to claim a free one-way ticket on the easyJet network, including destinations in the Middle East and North Africa.

The easyJet chief executive, Carolyn McCall, said: "It shows our confidence in our operational robustness and that we believe that flexi fare as a product will do well."

A flexible ticket on the airline typically costs two or three times more than a normal easyJet trip; on a Gatwick-Amsterdam flight a month from now, the regular price is £50 while a "flexi fare" is £143. But the latter also buys the right to change flights, and comes with speedy boarding and baggage privileges. Over this summer, one in six flights arrived at least 15 minutes late, which potentially exposes easyJet to a large number of claims. But serious disruption caused by weather, volcanic ash or industrial action beyond the airline's control are excluded from the deal.

The redemption terms are generous for an industry with a reputation for awkward small print. The free flight must be booked at least a fortnight before departure and taken before the end of March next year, and key Christmas/New Year and half-term dates are excluded.

A spokesman for British Airways shrugged off the development, saying "Flying is always sweet with BA. No charge for food and drink. No charge for choosing your seat the day before you fly. No charge for checking in a 23-kilo bag. No charge for booking by debit card. And no gimmicks."