Britain and Finland are discussing plans to require third parties to do more to block the Russian shadow oil tanker fleet operating in the Baltic and the Channel, the Finnish foreign minister has said.

The waters around Finland act as a key choke point for the estimated 100 Russian-bought oil tankers that navigate the Baltic monthly using opaque ownership structures to carry 90m tonnes of oil.

Elina Valtonen said the EU was looking at a further package of sanctions but added: “What is very important is that the G7 is active in this as well because obviously what the shadow fleet is doing is circumventing the oil price cap.”

Valtonen, who became foreign minister in the new centre-right government last year, was in London to sign with the UK foreign secretary, David Cameron, a strategic partnership that reflects the growing ties between the two countries recently cemented by Finland’s decision to join Nato, a move that extends the defence alliance’s borders with Russia by 830 miles.

Valtonen, a fluent German speaker, also laid out new domestic legislation that she said could act as a model for the rest of Europe to fend off what Finland believes is an attempt by Russia to destabilise her country by forcing third country nationals over the border. Critics say the new law gives too much discretion to border guards, restricts rights of appeal and contravenes the European convention on human rights. Finland has closed its border with Russia.

A $60 a barrel price cap on Russian oil imposed in December 2022 was designed to deprive insurance from a tanker transporting oil at above the price cap. The aim had been to restrict the flow of revenue to the Russian war machine while at the same time not causing a huge spike in oil prices that could weaken the world economy.

Valtonen said there was evidence the shadow fleet ignored insurance demands, adding: “We are looking at several ways of making life harder for their ships, but also for those countries under whose flags they are operating.”

She said: “We need to find solutions, not just as the EU, but collectively together with our partners and allies around the world to find ways effectively to put an end to this because it’s obviously not just an environmental risk, but also it’s a way for Russia to keep on exporting its oil and getting hard currency for its economy.

“We will make use of international organisations and also see to which extent the international maritime law allows us to effectively prohibit such traffic.”

It is estimated that in the first quarter of this year 33m barrels of oil in uninsured ships travelled through the Viro strait between Estonia and Finland.

Valtonen said new forms of enforcement were needed but added: “It’s just not very easy because international maritime law is basically geared towards opening navigation and making it very difficult for any country to intervene with free traffic. The law was built for a completely different world than what we are now looking at.”

Many Baltic and Nordic countries are nervous of apprehending ships suspected of being unseaworthy, fearing it would lead to a naval confrontation with Russia.

Valtonen also called for tougher measures to block Russia’s instrumentalisation of migration.

“We have evidence of Russia not only mobilising typically third country citizens, within their borders, but also from within Russia towards our border. We can’t have an outside power, self-declared to be hostile towards Finland and the west, that decides on our behalf who is to enter Finland.

“So we have used these few months to draft legislation, which would allow us to more flexibly counter this aggression by Russia, and this legislation could indeed be used as a blueprint for the rest of Europe as well, because all border nations with Russia and Belarus are facing this.”

She said southern European states were confronting the same crisis.

Speaking at the Finnish ambassador’s residence next door to the Russian ambassador, she said the west had to accept Russia was aggressive for the foreseeable future and the only way to protect itself was to become stronger in deterrence.