Foreign Secretary William Hague said the charter plane, which would be despatched within the next 48 hours, would be accompanied by a "rapid deployment team" of ministry officials.
The Royal Navy frigate HMS Cumberland would be redeployed from the eastern Mediterranean so that "it is pre-positioned in case it is required to play a role in assisting British nationals," Hague said in London.
The government was also working closely with airlines to assist as many British nationals as possible to depart Libya, he said.
"Already this week British nationals seeking to leave Libya have encountered significant difficulties," said Hague.
Many were currently at Tripoli airport without immediate flights out of the country following flight cancellations and closures of airspace.
Meanwhile, British Airways (BA) Tuesday cancelled its return flight to Tripoli due to the unrest in Libya.
The airline, which operates a daily service to the Libyan capital from London's Heathrow airport, said it would make a decision Wednesday's flight later.
Meanwhile, former prime minister Tony Blair, who played a leading role in Western efforts to restore diplomatic and trade links with Libya over the past decade, Tuesday condemned the "totally unacceptable violence" in the country.
However, he also defended his previous policies towards the regime of Gaddafi, which led to Libya renouncing the development of Weapons of Mass Destruction (WMD)- and terrorism.
"There's clearly been a huge benefit externally of the change in Libya's position from a state that was developing nuclear and chemical weapons and sponsoring terrorism to a state that in 2003 gave up WMD and is now cooperating in the fight against terror," a spokesman for Blair said.
"However, none of that justifies the violence internally. The pictures from Libya have been shocking and appalling. Such violence is totally unacceptable and that is why there is an urgent need for a process of political change," he added.
In London, up to 1,000 noisy protesters Tuesday called on the British government to take action to oust Libyan leader Muammar Gaddafi.
The demonstrators, mostly anti-Gaddafi Libyans, gathered at the gates of Downing Street, the seat of the British government, in central London.
"Act now before genocide in Libya" and "No action = approval," said their posters. Shouting in English and Arabic, they demanded: "Stop killing people now" and "God help us oust Gaddafi."