The Government has advised against all but essential travel by air to Sharm el-Sheikh airport after concluding there is a "significant possibility" an explosive device caused the Russian jet crash in Egypt.
Foreign Secretary Philip Hammond said all UK passenger flights to Sharm el-Sheikh had been cancelled as a result.
Earlier, flights from Sharm el-Sheikh to the UK were delayed amid fears about an explosive device causing the deadly crash, which killed all 224 people on board Russian operated Metrojet flight KGL9268.
Following an emergency COBR meeting chaired by David Cameron, Mr Hammond said: "We have concluded that there is a significant possibility that the crash was caused by an explosive device on board the aircraft.
"We are now advising against all but essential travel by air through Sharm el-Sheikh airport. That means that there will be no UK passenger flights out to Sharm el-Sheikh from now."
A team of UK aviation experts have travelled to the Egyptian airport to carry out a security assessment there.
At the COBR meeting, the Prime Minister was provided with their initial assessment, which concluded that although Egyptian authorities had stepped up security efforts, more needs to be done.
Downing Street said it was working to arrange flights back to the UK for people already in Sharm, but that there would be none on Thursday.
Flight KGL9268 crashed in the early hours of Saturday while travelling from the Red Sea resort of Sharm el-Sheikh to St Petersburg, Russia.
Investigators have been working to establish what caused the passenger jet to crash and have begun examining the plane's two 'black box' flight recorders, although Egypt's Civil Aviation Ministry has said the recorder collecting data from the cockpit was "partially damaged".
Theories on what might have happened vary between authorities in Russia, where the flight's operator is based, and Egypt, where it crashed.
Egyptian leaders have stated claims by Islamic State-linked militants that they were responsible were "propaganda" while the Kremlin has refused to rule out terrorism as a possible cause.