Norway could block the UK if it tries to rejoin the European Free Trade Association (EFTA), the small club of nations that has access to the EU single market without joining the EU itself.
Senior Norwegian government members are to hold talks with David Davis, the UK minister responsible for overseeing the UK exit from the EU, in the next few weeks.
Some Brexit supporters have suggested the EFTA would be a way of retaining access to the EU single market while honouring the referendum mandate to leave the union.
Norway is not a member of the European Union but has access to Europe's lucrative single market via its membership in the European Economic Area (EEA), which groups all EU members and three of the four EFTA members (Norway, Iceland and Liechtenstein, but not Switzerland).
Norway's European affairs minister, Elisabeth Vik Aspaker, reflecting a growing debate in the country following Brexit, told the Aftenposten newspaper: "It's not certain that it would be a good idea to let a big country into this organisation. It would shift the balance, which is not necessarily in Norway's interests."
She also confirmed that the UK could only join if there was unanimous agreement, thereby providing Norway with a veto. She added she did not know the UK’s plans.
EEA membership requires access to the four EU freedoms: free movement of persons, services, goods and capital. Norway, in need of extra labour, does not oppose free movement, though the subject of asylum seekers and refugees is controversial.
The EU special summit in Bratislava and the Conservative party conference in October might provide greater clarity on UK thinking, Ms Aspaker said.
One concern is that Norway, through the EFTA, has signed trade agreements with 38 countries, including Mexico, Canada, Colombia, Morocco, Kuwait and Qatar. If the UK joined, those trade agreements might have to be renegotiated, and future trade agreements would become more complex.
During the UK referendum campaign Norwegian government members including the prime minister, Erna Solberg, repeatedly urged British voters not to follow the Norway example saying: "Do not leave the EU, you will hate it."
The largely pro-EU political class in Norway argue the high price for access to the EU single market is a loss of sovereignty since Norway is bound by EU decisions without having a vote on how they are taken.
Britain was a founding member of EFTA in 1960, a free trade organisation that was an appendage to the European Economic Community (EEC), the forerunner of the EU. In 1973, Britain joined the EEC.
Before the summer, Ms Aspaker set up an inter-ministerial working party within the foreign ministry to look into how to safeguard Norway’s interests.
Ms Aspaker has stressed the need to retain good co-operative bilateral relations with the UK. But there are concerns that if the UK joined the EFTA it would usurp Norway’s dominance of the small club, or may demand changes to the terms of the agreement.
Norwegian Labour party officials are due to travel to the UK Labour conference this autumn for talks on future relations with the EU.
Jeremy Corbyn told his party at the weekend it needs to accept the vote to leave the EU, but has suggested the possibility of Norway-style access to the single market.
Audun Lysbakken, the leader of Norway’s Socialist Left party, has argued that the EEA agreement should be renegotiated, with the UK’s help, saying countries “outside need a better model for cooperation with the EU than the current EEA agreement”.
He added he was amazed his government did not want to have an open debate about a new relationship with the EU. He said: “Throughout the spring, the government has been adamant that the EEA is not a good model and it is not something they would recommend to the British. Now they suddenly want to leave it as it is.
“The EEA has created a significant democratic deficit through importing laws over which Norway has little influence.”
Polls in Norway have suggested Norwegian voters are divided over whether Brexit will be good for Norway or the beginning of the end for the EU. Nearly 70 per cent oppose Norway seeking to join the EU.