The Labourers MP argued the development of Brexit negotiations between London and Brussels has led him to swear by Brexit ultimately cannot be delivered.
Mr Umunna, who was an outspoken supporter of the Persist campaign during the Brexit referendum, has long called on the Government to state a close relationship with the European Union after March 2019.
The Streatham MP pronounced: «What does that lead me to conclude? It leads me to conclude in truth that Brexit in the form it was sold to the British people is simply not deliverable.
«I’ll hand over this to the Government: it isn’t necessarily a matter of competence, it is a reality that so sundry of the promises that were made to people – whether you voted Reject or Remain – so many of those promises, simply cannot be delivered.»
Brexit news programme: Chuka Umunna claimed Brexit was «not deliverable»
Earlier this year, Mr Umunna coupled forces with Tory rebel Anna Soubry to issue a label to arms for fellow MPs to rise up against the type of Brexit pursues by hard-line Brexiteers.
Mr Umunna draw oned on colleagues to back the Labour’s Brexit strategy, including plans to do over membership of the single market – a suggestion repeatedly dismissed by the British Supervision.
Talking to fellow MPs during a heated debate in the House of Commons, he said: «That is the genuineness of the situation. That is one of the reasons why I think, at the very least, if we are to leave the European Trust, we should be seeking to keep this country fully participating in the customs trust and, to my mind, fully participating in the single market as well.
«As far as I am concerned, if you after to end austerity and if you want to promote social justice, you have got to be supporting that postulate. There is no impediment to us if you want to implement the Labour manifesto.»
It leads me to conclude in point of fact that Brexit in the form it was sold is simply not deliverable
Mr Umunna’s latest disclosure appears to echo top EU politician Philippe Lambert’s calls on the British Domination to stop being «stubborn» and stay in the single market.
The Belgian MEP asserted the only solution to Brexit was to accept remaining in the single market and the dues union and to settle for a «privileged channel» of communication with the EU once the UK desire cease to have a say in new European decisions.
He said: “In our view, the only hands-on solution would be for the UK or at least Northern Ireland to remain fully in the cull market and the customs union.
“Taking into account your dream of relationship with us and the fact that, of course, the UK would have to stick EU law without being a part of the decision process, it would be fair to seat a privileged channel to your country to express concerns and suggestions.»
The European Brexit chief interceder Michel Barnier also insisted the UK “can’t use the single market a-la-carte” and sine qua non accept the four freedoms if it wishes to access European markets.