Britains opposition parties intensified attacks on Prime Minister Boris Johnson on Thursday with two weeks to go until election day, as polls suggested the UK leaders Conservatives have a substantial lead.

Jo Swinson, leader of the centrist Liberal Democrats, accused Johnson of spewing serial falsehoods and dragging the office of prime minister through the mud.

She said Johnson can't be trusted because he vowed to lead Britain out of the European Union by October 31 — and didn't — and said he would never ask the EU to delay Brexit — but did.

“Boris Johnson is not fit to be prime minister not just because he doesn't care, not just because he lies, but also because he is complicit in stoking division and fear in our communities,” Swinson told supporters during a speech in London.

Johnson has faced questions about his character throughout the campaign. The prime minister has a history of making offensive remarks, including a newspaper column last year in which he compared women who wear face-covering veils to letterboxes.

The main opposition Labour Party unearthed an article Johnson wrote in the conservative weekly magazine, The Spectator, in 1995 in which he called the children of single mothers ill-raised, ignorant, aggressive and illegitimate.

Johnson accused his opponents of trying to disinter and distort pieces that are almost 25 years old.

He has also been accused of dodging scrutiny. He is the only main leader not to have agreed so far to a one-on-one interview with BBC journalist Andrew Neil. He has also declined an invitation to take part in a TV debate on climate change onThursday alongside other party leaders.

Broadcaster Channel 4 said Johnson and Brexit Party leader Nigel Farage, who also declined to appear, would be represented onstage by melting ice sculptures.

Johnson insisted on Thursday that he would do many, many interviews over the course of the next few days and I'm sure that people are having all sorts of conversations right now about who I'm going to be talking to, when and where, and I look forward to it very much.”

With most polls showing a double-digit lead for the Conservatives, the party is keen not to make waves. Treasury chief Sajid Javid insisted the party was not complacent and would go out there and fight for every single vote.”

Labour, meanwhile, is struggling to satisfy supporters who oppose Brexit, as well as those who want to leave the EU.

The party says that if it wins the election it will negotiate a new divorce deal with the EU, then give voters a choice in a new referendum between leaving the bloc on those new terms or remaining.

A respected economic think-tank cast doubt Thursday on the spending pledges of both main parties, Conservatives and Labour, concluding that neither was being honest with voters.

The Institute for Fiscal Studies warned it was “highly likely” that a Conservative government would end up spending more than the party's platform implied, while Labour would not be able to deliver on a promise to raise investment and revenue without taxes beyond those already announced on the rich and on big business.

Neither is a properly credible prospectus, IFS director Paul Johnson said.

Parties court the approval of the IFS, seeking its imprimatur on their spending plans. But the think-tank concluded the promises didnt match the math.

The IFS analysis outlined the scope of the main parties drastically different views of the future, arguing the choice between the Conservatives and Labour could hardly be starker. With the exception of health, the IFS concluded that if the Conservatives formed the next government, public spending would be 14 per cent lower in 2023-24 than it was when the party took office in 2010.

“No more austerity perhaps, but an awful lot baked in,” the IFSs Johnson said of the Tories.

Labour on the other hand, would raise both taxes and spending to peacetime highs. The party has pledged a sweeping expansion of the state, including the nationalisation of the railways and key utilities.

Labour would not be able to deliver investment spending increases on the scale they promise, the IFS director said. The public sector doesnt have the capacity to ramp up that much, that fast.

Britons will vote December 12 to fill all 650 seats in the House of Commons.

Johnson wants to secure a majority in the election so he can push through the Brexit divorce deal he negotiated last month with the EU. Under the terms of that deal, the UK would leave the EU on January 31 but remain part of the EU's single market, and bound by the blocs rules, until the end of 2020.