The Foriegn and Commonwealth Office has updated it’s advice on travel in Egypt:
We advise against all but essential travel to Cairo (all four governorates, including Giza), Alexandria, Luxor and Suez. The nationwide curfew has been extended from 1500-0800 local time. We recommend that British nationals without a pressing need to be in Cairo, Alexandria or Suez leave by commercial means where it is safe to do so. British nationals in other areas of Egypt where there are demonstrations should follow the advice below and stay indoors wherever possible.
Airlines are updating their advice, with BMI running a service to Cairo tomorrow on revised times and routes (with rebookings being given to end of March).
British Airways is operating services to change travel up till 28th February, or rerouting to Sharm El Shek.
Again – check with your carrier and safe travels.