Embassy officials in Yemen are being withdrawn from the country with "immediate effect", the Foreign Office has said.
The department said only a "small core" of staff will remain in the country, and it urged other British nationals to leave.
A spokesman said: "In light of the rapid deterioration in the security situation in Yemen and the high risk of increased tension in Sana'a and likely protests on Friday 25 March which might result in violent clashes, part of the British Embassy team in Sana'a is being temporarily withdrawn, leaving a small core staff in place."
The move comes as people have taken to the streets to protest against the regime.
Tensions intensified on Wednesday as the country's parliament granted President Ali Abdullah Saleh's request for sweeping emergency laws that include new powers of arrest, detention and censorship to quash the popular uprising demanding his removal.
It escalated the friction between Mr Saleh and a movement that now includes top military commanders, religious leaders and protesting youth.
Rival factions of the military have deployed tanks in the capital, Sana'a. In the most brutal show of force against anti-government demonstrators, security forces shot dead more than 40 protesters on Friday.
The Foreign Office has advised against all travel to Yemen since March 4 and have urged British nationals to leave the country immediately since March 12. It remains in close touch with those British Nationals who have chosen to remain in Yemen.
The British Government urged all parties in Yemen to exercise the "utmost restraint" and take all steps necessary to defuse the situation.
It said it was "crucial that all Yemenis play a responsible role in bringing about political and economic reforms" that respond to the legitimate demands of the Yemeni people and "build a peaceful and secure future" for the country.