Paul Nuttall was put on the back foot as he attempted to defend the UK's decision to leave the EU during the ITV leaders' debate on Thursday 18 May.
"People knew what they were voting for," the Ukip chief said, as he claimed Brexit voters wanted to withdraw from the EU's single-market.
But Liberal Democrat leader Tim Farron and Plaid Cymru head Leanne Wood pointed out that Norway was not a member of the EU, but had extensive access to its single-market as part of the European Free Trade Association.
Elsewhere, Nuttall urged Theresa May to be bold during the two-year-long divorce negotiations with Brussels and seek to dramatically reduce net migration to the UK. "The best way of dealing with it is an Australian-style points system," he said.
But like Labour leader Jeremy Corbyn, the prime minister had decided not to attend the event at MediaCityUk in Salford.
"May may not have the guts to be here tonight but her spokesman in Paul Nuttall has the bottle to stand in her place," SNP leader Nicola Sturgeon quipped.
The First Minister of Scotland added: "If you don't want Theresa May to have a free hand for a damaging Brexit, vote for a strong opposition."
The debate comes just three weeks before the general election on 8 June. The latest opinion poll from YouGov, of more than 1,800 voters between 16 and 17 May, put the Conservatives on 45%, Labour on 32%, the Liberal Democrats on 8%, Ukip on 6%, the SNP on 5% and the Greens on 2%.