Chuka Umunna said Jeremy Corbyn and Boris Johnson both pose a "threat" to the union of the United Kingdom.
The Liberal Democrat said last night's televised debate between the pair "exposed" the Prime Minister as wanting a hard border in Ireland, meanwhile, the Labour leader refused to say whether he would back Leave or Remain in a second referendum, and did not rule out another vote on Scottish Independence.
"Both of them in their own way clearly pose a threat to the union which is the United Kingdom," Mr Umunna told talkRADIO's Julia Hartley-Brewer.
"Boris Johnson was exposed for being responsible in his plans for definitely leaning to there being a form of hard bordern between the UK and Southern Ireland, and Jeremy Corbyn refused to rule out holding a second Scottish Independence referendum."
Mr Umunna, who is standing as an election candidate in the Cities of London & Westminster constituency, said viewers of the debate were presented with an "appalling choice".
"A huge part of the argument was absent from the room. There is a substantial proportion of people in this country who want to abandon Brexit and they were not represented in either Boris Johnson, clearly, or Jeremy Corbyn," he added.
"Thank goodness that is not the only choice that they have."
His comments come after the Liberal Democrats and SNP lost a High Court challenge against the exclusion of their leaders from the ITV debate.
However, an hour after the head-to-head debate was aired, another programme was shown on ITV featuring interviews with Liberal Democrat Leader Jo Swinson, Scottish National Party leader Nicola Sturgeon, Brexit Party leader Nigel Farage and Green Party co-leader Sian Berry.
Chuka Umunna is standing in the election alongside Jill McLachlan (Christian Peoples Alliance), Nickie Aiken (Conservative Party), Zack Polanski (Green Party), Gordon Nardell (Labour Party) and Dirk van Heck (The Liberal Party).
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