Opposition politicians rounded on Prime Minister Theresa May Wednesday over her handling of Britain's departure from the European Union (EU).

May faced an avalanche of questions during the first session of Prime Ministers Questions following the summer closure of the Houses of Parliament.

The fiercest attacks came from the main opposition leader, Labour's Jeremy Corbyn.

But it was the Scottish Nationalist Party's leader at Westminster, Ian Blackford, who slammed her Brexit blueprint she unveiled after a summit at her Chequers summer retreat.

"Why is the Prime Minister gambling with Scotland's future by taking us out of the EU against our will with her disastrous Chequers plan," he asked May.

Blackford said the EU's chief Brexit negotiator Michel Barnier has said her Chequers plan is "not acceptable" while former Bank of England chief Mervyn King has called the government's preparations "incompetent".

"With the clock ticking down, will the Prime Minister finally concede that backing the single market and customs union is the only option to protect jobs, the economy and the Northern Ireland Good Friday agreement," he stormed.

May told Blackford: "The only people gambling with Scotland's future are those in the Scottish National party, who want to take Scotland out of the United Kingdom."

May repeated what she had already told Labour's Corbyn, adding "We have put forward a proposal, under the Chequers plan, that protects jobs and livelihoods, that ensures that we deliver on the vote of the British people and that ensures that we deliver on no hard border between Northern Ireland and Ireland and maintain the Union of the United Kingdom."

She said Barnier has put forward another proposal, which creates a border down the Irish sea. "I have said that it is unacceptable to me as Prime Minister."

Corbyn in his attack said to May: "The International Trade Secretary (Liam Fox) has said that he is unfazed by no deal; the new Foreign Secretary (Jeremy Hunt) said no deal would be a "huge geostrategic mistake"; and the Chancellor (Philip Hammond) wrote to the Treasury Committee stating that a no deal Brexit would slash GDP by almost 8 percent which is comparable with the global financial crash."

He asked May: "Which assessment does she agree with?"

May responded by saying the director of the World Trade Organisation (WTO) said that no deal would not be a "walk in the park" but it would not be the "end of the world".

"The government are right to make the necessary preparations for no deal while working for a good deal to ensure that we deliver on the vote of the British people, that we come out of the European Union on 29 March 2019, and that we do so in a way that protects jobs and livelihoods, ensures no hard border between Northern Ireland and Ireland and maintains the precious Union of our United Kingdom. On one thing I am clear: we are working for that outcome and we will not have a second referendum."

Earlier in a session on Northern Ireland, Labour politician Kerry McCarthy said a poll this week said that people in Northern Ireland would vote for a united Ireland if a hard border was put in place on the island of Ireland.

"Are not the government sacrificing the Union (Great Britain) on this altar? Would not the best solution be to move forward with plans to stay in the single market, stay in the customs union, avoid a hard border, and protect the people of Northern Ireland from Brexit?" McCarthy asked.

Northern Ireland minister Shailesh Vara replied: "It is our intention that there will be no hard border and no physical infrastructure. The people of this country voted in the referendum, and this government's intention is to make sure that we are not part of the single market or the customs union. The whole United Kingdom, including Northern Ireland, will be leaving those two institutions."

Although across Britain people voted in the 2016 referendum by a margin of 52 percent to 48 percent to leave the EU, there was a majority for remain in Northern Ireland.