Syria's presidential election, which delivered a landslide victory to Bashar Assad, "bore no relation to genuine democracy" and conferred no legitimacy on the dictator, Foreign Secretary William Hague has said.
Mr Hague said that holding the poll in the midst of a fierce civil war was "an insult to Syrians" who have been demanding political change.
The speaker of Syria's Parliament announced that Assad captured almost 89% of the vote in Tuesday's election, which was held only in Government-controlled areas, trouncing two regime-approved challengers.
In a statement issued in London, Mr Hague dismissed the outcome of the vote: "Assad lacked legitimacy before this election, and he lacks it afterwards.
"This election bore no relation to genuine democracy. It was held in the midst of civil war with millions disenfranchised, denied access to basic humanitarian aid, and with all opposition to Assad brutally suppressed.
"Holding an election in such circumstances is just a way of sustaining his dictatorship, and is an insult to the Syrians who have been calling for freedom and real political change."
Mr Hague urged Assad to engage with the peace process set out in UN-sponsored talks in the Swiss city of Geneva, which envisaged the creation of a transitional governing body with the consent of both sides in Syria's three-year civil war.
"Assad has no plan for peace, stability or reconstruction in Syria," said Mr Hague. "His only formula is the killing and starvation of his own people, the destruction of whole cities and the displacement of millions. He is pushing Syria towards greater fragmentation and further misery.
"There is a clear route for Assad to end the conflict in Syria, he must engage with the UN-sponsored Geneva process which calls for a transitional governing body established with the mutual consent of both sides.
"The UK is increasing its support to those seeking a genuine political settlement in Syria, including by backing the moderate opposition and their vision for Syria of true democracy, pluralism and respect for human rights."
Earlier, US secretary of state John Kerry sharply criticised the Syrian presidential vote as "a great big zero" and said it cannot be considered fair "because you can't have an election where millions of your people don't even have an ability to vote".