The former British Prime Minister Gordon Brown has joined growing calls for holding a second Brexit referendum in the country, proposing an extension to the transition period due to due to no deal being reached by March.

"I believe there will be a referendum on Brexit. What I'm not sure about is when it will be," he said during a speech at the inaugural memorial lecture in Edinburgh, The Guardian reported.

Just six months before Britain is due to leave the EU, the two sides differ on their view of the talks, the bloc says a withdrawal deal is within reach, while British officials say "big issues" still lie in the way of any agreement. May is trying to clinches a deal but there is uncertainty on whether she could sell it at home, where she will need approval from the British parliament.

They do agree on one thing, that time is running out to seal a deal to pave the way for Britain's divorce, the biggest change in trade and foreign policy for more than 40 years. As that departure date creeps closer, those wanting to influence May's approach to Brexit are intensifying their efforts.

One of the biggest hurdles is an agreement on the so-called Irish backstop to prevent the return of a hard border between the British province of Northern Ireland and EU member state Ireland if there is no immediate trade deal.

A seamless border is part of the 1998 settlement which largely ended decades of sectarian violence in the province. May is also committed to preserving "frictionless" trade with the EU after Britain leaves. Neither side has indicated there has been a deal on the Irish backstop. But after meetings in Brussels, Northern Ireland's Democratic Unionist Party, which props up the minority Conservative government in parliament, has issued a series of terse warnings to May.

The former Labor leader Tony Blair added his voice to calls for the party to vote down May's Brexit divorce deal, saying there was a 50-50 chance of holding another referendum. The 2016 referendum resulted in a 52-48 percent victory for the Leave campaign.

"Whatever Brexit is on offer today is going to result in significant economic harm," Blair, who served as prime minister from 1997 to 2007, told Reuters. "I still believe it is possible that Brexit is stopped, I think there is no majority in parliament for any proposition that the prime minister brings back," Blair said, adding that he wanted a second referendum.