European political leaders and diplomats have reacted furiously to the suggestion that Britain could leave the EU without paying a multibillion pound “divorce settlement”.

The European commission, along with 27 EU member states, have settled on a sum of about €60bn (£52bn) that the UK would have to pay to fulfil the commitments it had signed up to as an EU member.

In a report published on Saturday, the House of Lords EU financial affairs subcommittee argued that the British government would be on strong legal ground if it chose to leave the EU without paying anything, and suggesting that Brussels would have no realistic chance of getting any money.

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Responding to the development, the leader of the socialist group in the European parliament, Gianni Pittella, who will play a significant role in shaping the EU’s negotiating stance, accused the British prime minister of incompetence and a “bullying” attitude, warning Theresa May that her plans would soon hit reality.

“Theresa May is a bull in a China shop,” he said. “She likes playing the role of the hardliner, but she’s just coming across as fully inadequate to live up to this incredibly delicate historical phase.

“Against this background, it is extremely important that the UK is called upon to honour all financial obligations falling due, up to and including the date of its withdrawal.”

It has been reported that British government lawyers have privately concluded there is no law or treaty that can compel the UK to make payments to the EU after Brexit.

The European commission’s chief Brexit negotiator is expecting the UK to pay into the EU budget in 2019 and 2020, though there may be liabilities to pay as late as 2023. Payments for EU-funded infrastructure projects are not settled until two to three years after being agreed.

Pittella said that unless Britain settled its bill, there could be no progress on negotiating a free trade agreement with the EU. “Without an agreement on this and other crucial issues, talks on future relationships between the EU and UK cannot start. Madame May is fully aware of this, but she’s still fooling herself that the EU can be impressed by her bullying attitude.

“The reality will soon wake her up. Negotiations between the European Union and UK should be concluded in good faith and a spirit of mutual respect to ensure the orderly exit of the UK from the EU.”

One high-ranking diplomat for an EU member state said that May appeared to be making a ”an error in logic”. “This is not the price of leaving, and it shouldn’t be represented as that,” the diplomat said. “This is simply what the UK owes. If you buy a pint in a bar, you have to pay for it even if you don’t drink it.”