A trade agreement with the EU cannot substitute for Brexit because it is like trying to “blow up a bridge without bankrupting yourself”, a leading negotiator has warned MPs.

Canada’s legal counsel during its long trade talks with Brussels poured scorn on claims that such a deal could ever deliver the same benefits as membership of the single market and customs union.

Michel Barnier, the EU’s chief Brexit negotiator, has said Theresa May’s “red lines” mean the most likely deal on offer will be similar to the CETA agreement with Canada.

However, Cristophe Bondy, Ottawa’s counsel – while arguing CETA had delivered strong benefits for his country – warned Britain’s starting point, as an EU member, was completely different.

“A free trade agreement is like two parties on either side of river and they are considering building a bridge across that river because they believe it will be in their economic benefit – and that is what CETA does,” he told the Commons Brexit Committee.

But he added: “What the UK situation with the EU right now is that that bridge has been there for 45 years. Communities have been built up on either side of it. There are buildings on the bridge.

“And you are deciding what part of it you want to blow up without bankrupting yourself. It is an issue of what part of it you are going to keep if you can.”

Mr Bondy also rejected ministers’ hopes of a quick-fire deal with the EU, warning: “I see it descending into a lot of political acrimony.”

He echoed criticisms that, unlike Canada, Britain was “asking to have the benefits of being part of the club, but not play by all the rules”.

Brexit: the deciders Show all 8 1 / 8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

“You are not asking for the same thing from the start – I’m not asking what the UK is asking for frankly,” Mr Bondy added.

David Davis, the Brexit Secretary, has said he hopes to strike a “Canada Plus Plus Plus” agreement, adding on services – in particular financial services, to protect the City of London.

However, EU leaders will resist any attempt by the UK to protect its crucial financial services industry while ending free movement of labour as an attempt to “have your cake and eat it”.

In his evidence, Mr Bondy agreed with Mr Barnier that an agreement modelled on Canada’s is a “statement of fact” within the limits of the UK’s red line – which include ending free movement.

Other key hurdles for the Prime Minister were that Britain would have “less negotiating weight” with other countries, as a lone participant – without the muscle of the EU.

And there would still be a need for “borders and checks on products”, he warned. EU countries would need to know “where do they come from, do they meet rules of origin?”

“If you have a free trade agreement approach, you will have barriers at the border,” Mr Bondy warned.