British Airways has suspended flights to Cairo for seven days starting today to allow for an assessment of security there.
In a statement the operator said: "We constantly review our security arrangements at all our airports around the world, and have suspended flights to Cairo for seven days as a precaution to allow for further assessment."
Passengers were only told of the cancellation when they arrived at at Heathrow Airport today.
Official Foreign Office advice, updated yesterday, says: "There’s a heightened risk of terrorism against aviation."
Three Egyptian airport security sources told the Reuters news agency that British staff were checking security at Cairo airport on Wednesday and Thursday.
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A spokesman for Cairo airport told the BBC the airport had yet to be notified by BA of any such changes.
When asked for more details about why flights had been suspended and what security arrangements the airline was reviewing, a spokeswoman for British Airways responded: "We never discuss matters of security."
Christine Shelbourne, 70, from Surrey was due to go to Cairo for a week on Saturday with her 11-year-old grandson. Her boarding card would not let her through the check-in gates.
She told the BBC: "The check-in staff reissued my boarding pass and I tried again but that didn't work either and we were told to try again in half an hour.
"Whether they knew anything I don't know but my husband told me the flight had been cancelled before they did. There were no suggestions or help from staff about alternative flights."
"My 11-year-old grandson is heartbroken - he's been looking forward to the trip for months."
A letter to passengers from British Airways, posted on Twitter, reads: "We are sorry to inform you that your flight from London Heathrow to Cairo has been cancelled.
"We constantly review security arrangements at all our airports around the world and have suspended flights to Cairo for seven days as a precaution to allow for further assessment."
Hotel vouchers have been offered.
Official Foreign Office travel advice for Egypt was updated on Friday.
The Foreign and Commonwealth Office (FCO) advise against all travel to the Governorate of North Sinai, due to continuing criminal activity and terrorist attacks on police and security forces that have resulted in deaths.
One line from the advice says: "There’s a heightened risk of terrorism against aviation.
"Additional security measures are in place for flights departing from Egypt to the UK."
The Foreign Office advises against all but essential travel by air to and from the Egyptian resort of Sharm el-Sheikh, but has not issued similar warnings against air travel to and from Cairo.
British Airways is one of two airlines flying nonstop between UK and Cairo - the other is EgyptAir whose flights are continuing as normal.
