UK to send charter plane to Egypt
The Foreign Office is sending a charter aircraft to Egypt to provide additional capacity for those who may want to leave the country.
A spokesman described the situation in Egypt as "fluid and unpredictable".
The flight, which will arrive in Cairo later and return to the UK on Thursday, will provide 200 seats.
As mass protests continue David Cameron has told Egyptian Prime Minister Ahmad Shafiq the country "must... listen to the aspirations of its people".
Egyptian President Hosni Mubarak later said he would not stand for re-election in September.
Speaking on state TV, Mr Mubarak promised constitutional reform, but said he wanted to stay until the end of his current presidential term.
Foreign Secretary William Hague has told MPs that Egypt needs to have a broad-based government that will allow an orderly transition in the country - a view that was reiterated in the prime minister's discussions.
The Foreign Office believes existing scheduled airlines have enough capacity to carry Britons wanting to leave Egypt but it is putting on the additional charter as a precautionary measure.
Passengers will be charged £300, roughly the same amount as a seat with a commercial airline would cost.
Britons who wish to use the service are being asked to register with the Foreign Office.
Meanwhile, Downing Street said the UK government had had a "range" of conversations about the situation in Egypt, including a call to King Abdullah of Saudi Arabia.
In his discussion with Mr Shafiq, Mr Cameron "welcomed the restraint the Egyptian Army had shown [during Tuesday's demonstrations] and emphasised the importance of allowing the protests to take place peacefully", said Number 10.
"[He] also said that bold steps were needed to produce real, visible and comprehensive change, with a clear path to free and fair elections."
Downing Street added that the British Ambassador in Cairo, Dominic Asquith, had spoken to both government and opposition figures on the ground, including one of the protest leaders, Mohamed ElBaradei, in which he stated the same approach.
Speaking in the Commons, Mr Hague said Egypt had played a "positive and moderating role" in the region over 30 years and it was of "paramount importance" it continued to play such a role.
The Foreign Office has warned against all non-essential travel to Cairo, Alexandria, Suez and Luxor.
The travel advice also recommended that British nationals without a "pressing need" to be in Cairo, Alexandria or Suez should leave.
There are an estimated 20,000 British tourists in Egypt, the majority of them in the Red Sea resort of Sharm el-Sheikh, which is more than eight hours away from where the majority of the troubles are.
Another 10,000 Britons are thought to be living or working in the country.
Travel operators have confirmed the majority of their customers are in Sharm el-Sheikh.
A Foreign Office spokesman said: "The safety of British nationals is paramount. The situation in Sharm el-Sheikh remains calm. We have an honorary consul and a team of consular staff in Sharm el-Sheikh who are monitoring the situation.
"Clearly, any change in the situation will be reflected in our travel advice and we will act accordingly."
Earlier, a senior Conservative MP Patrick Mercer said the Foreign Office should change its travel advice.
He said: "The situation is really quite grave over in Egypt. We've got tanks on the streets. We've got infantry with bayonets fixed and yet we still have this rather ambivalent advice from the Foreign Office, whilst other nations are bringing their nationals out quite quickly."
Mr Mercer said he was amazed to see that travel agents were still advertising "cheap and very attractive holidays in Egypt", adding that people should be withdrawn from Egypt rather than encouraged to "go into this situation".