France has mocked Boris Johnson’s claim that the UK can have an Australia-style deal with the EU after Brexit as “for the birds”, warning an extra six months may be needed to strike an ambitious trade deal.

Its European affairs minister told an audience in London that such a deal did not exist and it was time for both sides to realise the next phase of Brexit was “for people … not for politicians”.

Amélie de Montchalin also warned that the EU would not be pressured into signing any trade deal by an “artificial deadline” created by Johnson, and if Europe needed an extra six months to achieve a good deal for both sides then that is what should happen.

In a speech to Chatham House, she indicated that France was prepared to take a robust approach to the UK’s decision not to extend the transition period beyond December.

She said it would be virtually impossible to do a deal in 11 months if the UK were to diverge completely on regulations, as that would require a hugely complicated “line by line” negotiation on tariffs and border controls.

The only way to achieve a deal in the time given was through close regulatory alignment, she said, warning that a crash-out would be the UK’s choice and not the EU’s.

“We are not ready to sign any kind of deal on 31 December at 11pm.

“We cannot let our level of ambition be affected by what I would call an artificial deadline. If the UK decides to shorten the negotiating period, it will be the UK’s responsibility. It will not be our choice on the European side,” she said.

The prime minister has repeatedly projected a readiness to crash out at the end of the year, claiming that if talks collapsed the UK would at least have an “Australia-style deal”.

This has been rubbished by many who point out that Australia does not have a deal with the EU and therefore this is just a euphemism for no deal.

“The idea that they’re good to be an alternative to a free trade agreement, an honest level playing field, based on the Australia model (which by the way does not exist) is for the birds as you say in the UK,” De Montchalin said.

She mocked the UK’s rejection of the notion that the geographical proximity of the EU and the UK was a valid argument for a “special relationship” that did not look like a Canada- or Australia-style deal.

“Our future relationship will necessarily be a special relationship. You are not Canada, you are certainly not Australia, first of all because you can get here by train.

“You are the United Kingdom and no matter what happens the UK will remain a strong economic power on the doorstep of the EU, geographically and economically.

She said if the UK wanted a special relationship with the US it would still have to take account of the distance between the two nations.

“Paris and London are 300 miles apart. Boston and London are 3,000 miles away. It [a US trading relationship] could be more difficult,” she said.

Her comments come a day after the UK unveiled its own negotiation mandate, warning that it would prepare for no deal if an agreement did not look likely at a stock-taking exercise in June.

She emphasised that the UK must remember that when it was negotiating with the EU it was negotiating with 27 member states, which like the UK were “sovereign” nations that had to protect the interests of their own citizens.

If the UK were to recognise that it was sovereign states in play rather than an enemy EU, then a space would be opened up for a deal, she indicated.

The issue of state aid, which is expected to be the subject of a major clash, was a case in point, she said. While the UK wanted to be free to give subsidies to British businesses without any deference to the EU, it was in both sides’ interests to have an agreement in this area.

“Businesses will not invest in the UK if they are not protected by massive subsidies in the EU. It does not make sense. So this whole thing about reciprocity is important,” she said.