Foreign Secretary William Hage has said he would send "as many planes as necessary" to evacuate British nationals from Libya.
Up to 300 Britons are struggling to leave Libya after scheduled flights were cancelled by commercial operators.
"We will send as many planes as necessary to bring home British nationals," Mr Hague said in a statement.
"Our preference clearly is for people to be able to leave on commercial flights as they have been doing. Or on our specially-arranged charter flights as they will now be able to do, rather than to send in military flights without permission, which is obviously riskier for the safety of all those involved. Although we don't by any means rule out doing that."
He added: "Britain does not rule out sending military flights into Libya without permission to evacuate stranded British nationals."
Amid criticism of the Foreign Office's response to the crisis, Mr Hague said a specially-chartered flight was currently on its way to Libya, a second would depart later in the evening and a third would be sent on Thursday morning if necessary.
The Foreign Secretary said Royal Navy frigate HMS Cumberland was also on its way to the chaos-stricken country.