More than 2,000 British Airways passengers had their tickets cancelled because the prices were too cheap, according to a travel agent.
Travel Up boss Ali Shah said he believes another five agencies also sold tickets due to the airline’s error.
BA has apologised for the error on flights to Tel Aviv and Dubai but declined to say how many were affected.
Customers said they were angry their tickets are not being honoured.
Shah told the BBC that flights normally costing more than £200 were advertised for £1 plus airport taxes, which can be several hundred pounds, between 5.45pm BST on June 11 and 11am the following day.
The agent, who said more than 2,000 of his customers have been affected, said: “It’s very cruel for the customers because they have booked these flights in good faith and expected it to be honoured.
“But I can also understand British Airways’ position, it’s a human error.”
Shah said all affected customers are being contacted and BA will provide a full refund as well as a £100 voucher.
Travel Up customer Ash Dubbay, from London, said he had booked a return flight to Tel Aviv for £195 but now has to pay about £1,000.
Several people contacted by the BBC said they had not been informed of the cancellation and only found out when they checked their online accounts.
They also said the £100 voucher was “useless” as, aside from “restrictive” terms and conditions, the flights were now costing much more than that.
BA said in a statement: “Errors like this are exceptionally rare, and if they do occur, under contract law, there is no binding contract between the parties.
“We have apologised to customers and offered a gesture of goodwill.”