The UK’s offshore financial centres must fall in behind plans to stop “dirty money” by publishing registers of corporate ownership, leading political campaigners have said, as Labour pledged not to cave in to lobbying designed to weaken the proposals.

Labour’s Dame Margaret Hodge and the Conservative MP Andrew Mitchell hit out at “dither and delay”, ahead of this week’s summit between UK government officials and overseas territories, such as the British Virgin Islands (BVIs) and Cayman Islands, in London.

In an editorial for the Guardian, they accuse overseas territories and crown dependencies, such as Jersey and the Isle of Man, of trying to water down or ward off measures designed to counteract money laundering and other illicit transactions.

“We know all too well that the overseas territories and crown dependencies play a pivotal role in helping crooks and tax dodgers launder and hide their dirty money,” Hodge and Mitchell said.

“Dirty money underpins corruption, crime and conflict. It causes immense harm at home and abroad, enabling serious and organised crime and diverting resources needed for vital public services.

“Public registers, and the scrutiny that they bring, are the best antidote to the scourge of illicit finance.”

Mitchell and Hodge are understood to have corralled support from dozens of MPs across the political spectrum to ramp up the pressure before the joint ministerial council. The two-day event starts on Wednesday.

“We must stop the dither and delay of recent years and pierce the veil of anonymity that protects criminals and kleptocrats,” they said.

The duo accused offshore centres of reneging on a promise to introduce public registers by December 2023.

A key point of contention is whether the registers would be open to everyone or only those with “legitimate interests”, such as anti-corruption campaign groups.

Some overseas territories are opposed to fully open registers and British lobbyists have been working with them in an effort to persuade the government to accept a “legitimate interest” compromise.

In an online briefing to the BVI financial sector, viewed by the Guardian, a lobbyist and a lawyer acting for the IFC Forum – an umbrella lobby group representing offshore law firms – told their audience of the need to “educate” Labour MPs.

Oliver Cooper, a Conservative councillor and a lawyer at Charles Russell Speechlys, who acts as counsel for IFC Forum, said the foreign secretary, David Lammy, and Stephen Doughty, minister for the overseas territories, had “been sold on […] the IFCs [international financial centres]”.

Stephen Doughty denied this. “I have been clear that where legitimate interest filters are implemented it must be to a high standard and as an interim step to full public accessibility,” he said.

“This will be key to bearing down on financial secrecy, which is the lifeblood of illicit finance including money laundering, and tax and sanctions evasion.”

During the briefing, Mitchell Cohen, a public relations executive at Lansons Team Farmer, said the offshore centres needed to engage with Labour to “detoxify any negative brands”.

He described Labour MPs sympathetic to Margaret Hodge’s position on registers as potential “forces of negativity” and said lobbyists needed to “neutralise” them with positive messages.

Cohen, who has advised several leading Conservative politicians and now advises the BVI government, said there was a hope that the Treasury would be open to stopping short of full public registers of beneficial ownership.

“We know Treasury are a lot more pragmatic and are going to be pulling a lot of strings across government,” he said during the presentation, given shortly after Labour won the election.

A Foreign Office spokesperson said the government was pursuing fully public registers with “full vigour”.

Hodge and Mitchell said: “If the overseas territories and crown dependencies will not accept the will of parliament we must use our powers to insist that they act.”

Hodge has previously called on the government to issue an “order in council” to compel overseas territories to comply and suggested the crown dependencies could be forced to follow suit, a proposal that would test constitutional convention and law.

A spokesperson for the Cayman Islands countered that there was “no evidence to back up any such claims with respect to illicit finance or sanctions evasion in the Cayman Islands”.

“It shows that money laundering cases involving the Cayman Islands are in fact extremely rare and that sanctions have been implemented effectively,” they said.

The Guardian also approached representatives of the BVIs, Jersey and the Isle of Man for comment.