Boris Johnson’s former Brexit negotiator David Frost has said the “weakness” of the UK’s position shaped the negotiations for the Northern Ireland protocol but blamed a lack of pragmatism in the EU’s approach for the current difficulties.

Frost said the deal he negotiated while in Johnson’s government would have run smoothly only if it had never been fully applied by the EU.

Writing in a foreword to a report by the centre-right thinktank Policy Exchange, he also challenged the Irish government’s focus on the “all-island” economy, which he said was not consequential but had become a political tool.

“Shaped as the protocol is by relative UK weakness and EU predominance in the withdrawal agreement negotiations, it enshrines a concept – the all-island economy – which suits the EU, Ireland, and their allies politically but which does not exist in real life,” Frost wrote in the foreword.

Boris Johnson is understood to be considering publishing a bill this week that would unilaterally override parts of the protocol, one which has sparked anger in Brussels and Dublin, amid an impasse between the parties at Stormont.

Frost said that applying the protocol should have taken into account the “economy reality” of trade between Northern Ireland and the Republic of Ireland, which the report says is minimal. Only 4% of the goods and services produced in Northern Ireland cross the border to the republic, while 16% go to Great Britain, and 31% of imports to Northern Ireland are from the rest of the UK, the report said.

“The protocol arrangements could only have worked if, in real life, the EU regulatory framework had not been fully applied in practice (recognising, for example, the protocol’s requirement to minimise checks and controls at Northern Ireland ports) and there had been much more pragmatism in its operation,” he wrote.

“As it was, the EU’s purism and its casually destructive handling undermined east-west links from the start and are now bringing the Belfast (Good Friday) agreement itself into great peril.”

The former Northern Ireland first minister Dave Trimble, who was leader of the Ulster Unionist party at the time of the Good Friday agreement, agreed there had been a “destabilising effect” by talking about the all-island economy.

“Today the Irish government has a different language in which the island economy is an endlessly repeated theme,” Lord Trimble said. “The Irish government sharpens unionist fears that there is some all-island economic propulsion leading to political unity. This has had a destabilising effect.”

Nick Thomas-Symonds, the shadow international trade secretary, said: “Now is not the time for a blame game about the workings of the protocol. What is needed is a pragmatic way forward.

“Chaos in the Conservative party should not be preventing ministers from getting around the table and carrying out the painstaking work necessary to find a solution, and the EU should engage in a pragmatic spirit.”