The most recent advice from the UK Foreign Office is that it is best not to travel to most of Egypt unless you have to, and if you are there already to think about leaving. The advice doesn't cover all areas of the country; seaside resorts in the Red Sea area are considered safe, for example. If you go the FO website or click this article you can get a full list of the areas which are considered safe. As you can see from the list, most of these are holiday resorts where the recent protests and military action were not taking place.
The most notable violence has been in the centre of Cairo, and has spread to some other major cities like Alexandria. The position of the FO is that while many, even most places in Egypt may be relatively safe, just now the situation is very volatile and it is very hard to know if, or where, the unrest may spread.
Click here for more up to date advice.