The Egyptian government needs to clarify what it is doing in order to hand over power, Foreign Secretary William Hague has said.
He said "credibility of change has not yet been achieved", but also urged restraint from Egyptians.
Demonstrators have been angered by President Mubarak's announcement on Thursday that he will not step down.
Meanwhile, the UK Foreign Office (FCO) has said it is "deeply concerned" about a Briton missing in Egypt.
Foreign Office minister Alistair Burt said Hisham Morsi was last seen being removed from Tahrir Square on 31 January but it is unclear by whom and authorities have been asked whether they are holding him.
An FCO spokesman said: "Hisham Morsi is the only British national that we are aware of who is missing at the moment."
Mr Morsi, who is of dual British and Egyptian nationality, is understood to be about 50-years-old and based outside the UK, "probably in Cairo".
Egypt's military high council has promised to lift the country's 30 year state of emergency when the "current situation has ended".
The lifting of the state of emergency has been a key demand of the protesters.
The army said, in what it called "Communique No 2", that it "confirms the lifting of the state of emergency as soon as the current circumstances end".
It endorsed the transfer of President Mubarak's powers to his vice-president, General Omar Suleiman, and guaranteed a free and fair presidential election, constitutional changes and "protection of the nation".
Mr Hague said: "On the face of it, from the reaction of people in Egypt to the president's statement and everything that has followed from that, that credibility of change has not yet been achieved.
"I think the most important things for us to call for, outside Egypt, are restraint from all involved today and clarity from the government in Egypt about the way forward."
His comments come after the deputy prime minister, talking to Nicky Campbell on BBC Radio 5 live, said the process in Egypt should lead to a more democratic and open future for the country.
Mr Clegg said he could understand the "intense frustration" of people who had hoped for more from last night's presidential address.
However, he said the UK government would not be giving a "running commentary".
Meanwhile Foreign Office Minister Lord Howell has told fellow peers that the Egyptian army faces "grim options."
During a debate Lord Howell said one "obvious" option would be for the army to mount a military coup.
Another was that they could simply hope to control the crowds.
But a third option was for the military to be drawn into a clash "if massive numbers of people" tried to attack key institutions.
The minister went on to praise the reporting of events in the country, saying "very brave people" had covered the protests, but no-one could predict what was going to happen.