A senior EU official has urged Boris Johnson’s government to move on from Brexit and work with the bloc in the face of Russia’s brutal war against Ukraine.

Maroš Šefčovič, the European Commission’s vice-president who is in charge of UK relations, repeated his criticism of the government’s “illegal” plan to rip up parts of the Northern Ireland protocol, two days after the bill cleared its first hurdle in the House of Commons.

He also made his most direct appeal yet to London to turn the page. “It is high time we got Brexit done,” Šefčovič said, turning the prime minister’s 2019 election slogan against him. “In the face of Russia’s brutal and unjustified war against Ukraine, it is clearer than ever before that the EU and the UK are natural allies,” he added. “Where the rules-based order is under pressure, strengthening western unity should be our moral imperative.”

He was speaking at Bloomberg’s headquarters in London, where David Cameron launched his ill-fated attempt to renegotiate the UK’s place in the EU nine and a half years ago.

In that 2013 speech, the then Conservative prime minister said Britain would remain tied to the EU by a complex web of legal commitments. “If we leave the EU, we cannot of course leave Europe,” Cameron said – a line Šefčovič quoted as he appealed for “strong strategic EU-UK relations”.

In a pointed rebuke to the current prime minister’s shifting position on the Brexit withdrawal deal signed with the EU in 2019, Šefčovič said: “I agree with prime minister Johnson’s assessment from 2019 that the protocol is fully compatible with the Good Friday (Belfast) agreement.”

Under the Brexit withdrawal agreement, Northern Ireland largely remains in the EU single market to avoid a hard border on the island of Ireland.

The Slovakian official said the protocol offered Northern Ireland the best of both worlds, or “having the jam on both sides of the bread”. Under the agreement the region can trade easily with the EU, as well as benefit from any trade deals the UK signs with the rest of the world.

He accused the government of a failure to engage, which he said was “extremely disappointing as a majority of people in Northern Ireland can appreciate the positive benefits and opportunities that the protocol brings”.

An opinion poll for Queen’s University Belfast, published on Wednesday, showed that 55% of people in Northern Ireland think the protocol is a suitable arrangement, although 59% thought it was having a negative impact on political stability in Northern Ireland and on British relations with the Irish republic.

Šefčovič repeated his offer to cut protocol red tape, but said it was “unrealistic and unfair” for London to expect all barriers to be removed when goods travel to Northern Ireland from the rest of the UK.

The government has said businesses should be able to choose between a British or EU regulatory regime, which Šefčovič said would “bury them under a mountain of bureaucracy”.

Privately, commission officials have voiced scepticism that the Northern Ireland protocol bill will ever become law, although Johnson predicted it will be on the statute books by the end of the year.