Air tickets have spiralled in price as a result of the BA dispute, leaving passengers facing the prospect of paying hundreds of pounds more for trips.
Travel agents said few seats were available for short and long-haul destinations this weekend, the start of the Easter getaway for many families and the next planned walkout by cabin crew.
Under the booking system operated by airlines, the last few remaining seats on a plane are the most expensive. They can be several times the cost of the cheapest flights, adding a hefty surcharge to trips that may have been booked months ago.
Whether customers will have to pay for any increase depends on how they booked their ticket.
Customers who booked a flight only with BA, direct through BA or through a travel agent, will receive a full refund from BA in the event of cancellation, but will have to pay for any increase in fare required by another airline experiencing higher than usual demand.
However, if the flight was booked as part of a package with accommodation or entertainment, then, under EU package holiday regulations the tour operator will be responsible for re-arranging the schedule and paying any increase in cost. Rival airlines have been keen to capture any extra business caused by the BA dispute, increasing revenue from lucrative last-minute bookings when planes are almost full, and also giving them the chance to lure customers away from what was once Britain's favourite airline.
Ryanair last week launched a £69.99 one-way BA rescue fare, while BMI has been placing newspaper adverts with traffic lights showing a red light for BA and a green light for itself.
Lucy Balding, marketing assistant at Trailfinders travel agent, said BA's problems would cause extra problems at a peak time of year. "BA has huge capacity so with its cancelling flights there will be a lot more demand on other operators," she said.
"The airlines have not necessarily had to put their prices up but the prices are very much down to availability so when you are down to the last few tickets, those tickets will be much higher."
Trailfinders, an independent travel agency specialising in long-haul trips for independent travellers, has been searching around for flights to fill the shortfall caused by the cancellation of BA services.
"We have had a lot of clients booked on to BA flights that have been cancelled. We have contacted them as soon as we know a service is cancelled. We have been very busy with that."