Video report by ITV News correspondent Neil Connery
Foreign Secretary Dominic Raab said the vote was “fraudulent” and condemned the violence from the Belarusian authorities as they attempted to crack down on the protests.
Mr Raab’s comments come as thousands of factory workers in Belarus took to the streets and crowds of demonstrators besieged the state television headquarters following the August 9 result.
The Foreign Secretary called for an independent investigation by the Organisation for Security and Co-operation in Europe (OSCE).
He said: “The world has watched with horror at the violence used by the Belarusian authorities to suppress the peaceful protests that followed this fraudulent presidential election.
“The UK does not accept the results.
“We urgently need an independent investigation through the OSCE into the flaws that rendered the election unfair, as well as the grisly repression that followed.
“The UK will work with our international partners to sanction those responsible, and hold the Belarusian authorities to account.”
Mr Lukashenko has ruled the ex-Soviet nation with an iron fist since 1994, repressing opposition figures and independent news organisations.
He has rejected any possibility of repeating the vote that gave him a sixth term, lashing out at the West and declaring his country will “perish as a state” if the election is rerun.
On the ninth straight day of protests against the official results of presidential vote, Lukashenko flew by helicopter to a factory in the capital in a bid to rally support but was heckled by workers chanting “Go away!”
Facing the angry crowd, the 65-year-old former state farm director dismissed the calls to step down.
“I will never cave in to pressure,” Lukashenko told the workers, saying those who intend to go on strike could leave if they want.
“There will be no new election until you kill me,” he shouted, charging that the protests are ruining the economy and warning that the country will collapse if he steps down.
As he spoke, over 5,000 striking workers from the Minsk Tractor Works plant marched down the streets of the city, demanding that Mr Lukashenko cede his post to Sviatlana Tsikhanouskaya, the leading opposition candidate.
“Lukashenko is a former president. He needs to go,” said Sergei Dylevsky, the leader of the protest at the Minsk Tractor Plant, adding that Tsikhanouskaya is “our president, legitimate and elected by the people.”
The official results of the August 9 vote gave Mr Lukashenko 80% of the votes and Mr Tsikhanouskaya only 10%, but the opposition claimed the vote was rigged.
Mr Tsikhanouskaya has said protocols from precincts around the country showed her winning 60-70% of the vote.
A brutal crackdown on protesters in the wake of Sunday’s vote has left nearly 7,000 people detained and hundreds injured, as police dispersed the crowds of peaceful demonstrators with stun grenades, rubber bullets and clubs.
The fierce clampdown provoked widespread anger, forcing the authorities to back off, and police have stood back since Thursday, letting protests go uninterrupted.