The Islamic State group which commands an affiliate in Egypt’s Sinai Peninsula claimed it destroyed the plane, without providing details.
Other airliners from Britain and Western Europe are also bringing their nationals home, after several countries and airlines last week suspended new flights to Egypt because of the security concerns.
Foreign Secretary Philip Hammond warned that if those suspicions are true, there needs to be a rethink of security at airports in areas where the extremist group is active.
The suspension came after several days of statements by British and American officials that it was possible a bomb on board had brought down the Russia carrier Metrojet’s Airbus A321-200.
Cameron said “there’s still an investigation taking place in Egypt. We need to see the results of that investigation.”
The jihadist group had claimed on Saturday that it downed the Airbus in Sinai, where its Egypt affiliate is based, but provided no details, prompting scepticism about its involvement.
Mourners continued to come to St. Petersburg’s Pulkovo airport on Tuesday to lay flowers and leave paper planes and soft toys at the arrivals hall.
The Egyptian official, who spoke on condition of anonymity because he was not authorized to speak to the media, said he was a member of a technical inspection team that included two Russians.
Almost everyone on board the Airbus-A321-200 operated by the Moscow-based Metrojet airline was Russian; Ukraine said four of its citizens were passengers.
Al-Jazeera spokesman Hasan Salim Patel confirmed Baher Mohammed’s arrival in the Qatari capital, Doha, on Wednesday. He says he is in the country for a temporary visit.
The assault ships, which can each carry 16 helicopter gunships, 700 troops and up to 50 armored vehicles, were originally intended for Russia.
The Egyptian government has long been plagued by corruption allegations. El-Sissi routinely emphasizes that he is fighting corruption.
Egypt’s North Sinai has witnessed many violent attacks by militants since the January, 2011 revolution that toppled the ex-president Hosni Mubarak.
The peacekeepers, part of a force that monitors a 1979 peace treaty between Egypt and Israel, are based in the North Sinai region.
Voters outside Egypt for the first stage will cast ballots on Oct. 17-18, and the rest on Nov. 21-22. The period for candidates to register opens Sept. 1 and lasts 12 days.