LONDON (AFP) - Britain will work with Egypt's interim authorities despite not supporting the military intervention that toppled Islamist president Mohamed Mursi, Foreign Secretary William Hague said on Thursday.

Mr Hague insisted that Britain had to be "practical" in dealing with the situation after the Egyptian army forced Mr Mursi out of office and held him in detention after days of deadly protests against his rule.

"We have to work with whoever is in authority in Egypt," Mr Hague told BBC radio.

"We have to do that for the safety of British nationals, we have to do that because there are so many British companies there."

Mr Hague tempered his condemnation of the army's role in Egyptian politics by saying it was a "popular intervention".

"We will always be clear that we don't support military intervention but we will work with people in authority in Egypt. That is the practical reality of foreign policy," he said.

"This is a military intervention in a democratic system. We have to understand it's a popular intervention, there's no doubt about that in the current state of opinion in Egypt."

Britain on Tuesday warned its nationals against all but essential travel to most of Egypt and said those already in the country should consider leaving.

Egypt underwent several decades of British rule until independence in 1922, while Britain invaded Egypt along with France and Israel in the 1956 Suez crisis.