Norway’s minister for Europe has warned Britain of serious consequences for economic and security policy if it leaves the European Union.

Before a visit to London, during which he will meet Foreign Office ministers and officials, Vidar Helgesen, Norway’s minister for the European Economic Area (EEA) and EU affairs, told the Observer that his country often found it difficult to shape economic rules that affected Norway – often cited by Eurosceptics as a shining example of how a nation can thrive outside the EU – while not being a member.

He also said that at a time of “burning security crisis not seen since the cold war”, most key meetings were now being convened at EU level, rather than within Nato, and it was vital that the UK was there to shape decisions. The comments come as an Opinium/Observer poll shows that a majority (51%) would vote today to leave the EU.

Helgesen will expand on his view that the UK should not leave in a talk to the pro-EU campaigning group, British Influence, entitled, “The European Union: why one who has not joined thinks that WE should not leave.”

Largely as a result of its oil resources, Norway is one of the wealthiest countries in Europe, with a higher per-capita income than the vast majority of its member states. British Eurosceptics often say the Norwegian experience is evidence of how a country outside the EU, but enjoying the benefits of the single market through membership of the EEA, can prosper without having to commit itself to full membership. Helgesen said, however, that this arrangement often created frustrations and difficulties, which meant Norwegian ministers and officials spent a lot of time – sometimes without success – trying to find out what was going on in EU meetings that would affect their country directly.

“We [Norway] are fully integrated into the EU single market as members of the EEA, but what we don’t have is the right to vote on those regulations that are incorporated into our law when they are made by the council of ministers.”

On occasion, Brussels has sprung surprises that the Norwegians could not predict. The same kind of frustrations could well face the UK. “You would not have all those Brits staffing the commission where the decisions are made,” said Helgesen. “Britain being on the outside would obviously not have that amount of people on the inside. You would find it more difficult, as a result, to affect the regulations.”

THe said the current Norwegian government, a coalition between Conservatives and the Progress Partycorrect, which came to office in 2013, had found that the previous administration had “not done its homework” and paid insufficient attention to regional policy guidelines that were going through Brussels.

As a result, it discovered that Norway had to abandon an employment tax-deduction system that had worked well for sparsely populated areas in the north, resulting in negative effects on businesses which suddenly found themselves with much higher costs.

“It is up to the British to make the decision [as to whether they leave the EU], but I would not think that if the Norwegian model were applied, that this would be ideal,” Helgesen said.

Norway has held two referendums on whether to join the EU. The first, in 1972, saw the country reject membership by 53.5% to 46.5% of voters. A second ballot, in 1994, also favoured rejection, this time by the narrower margin of 52.2% to 47.8%.

If the Tories win the general election on 7 May, David Cameron has promised to hold an in/out referendum by the end of 2017, after trying to renegotiate the terms of British membership. Most Tory ministers and MPs would support leaving the EU if the status quo remains. Helgesen said it would not only be difficult for the UK outside the EU, it would also be bad for Europe, both in terms of economic and security policy for the region.

“I think there is now a receptiveness in the EU for smarter regulation, less regulation and the EU caring more about the big things and less about the smaller things,” he added. “I think Britain has very important inputs to make in that process. And I also think that Norway – and Europe – is better served by the UK continuing to be a member.

“We have a burning security crisis in Europe not seen since the cold war. At that time, Nato was the sole organisation shaping western security. Today, the European responses to Russia’s actions are predominantly being shaped in the EU. Nato as a military alliance is essential to our common security. But let’s be honest, the foreign and defence ministerial meetings in Nato are fewer and less frequent than the foreign affairs council meetings in the EU.

“As a consequence, the EU provides the main ongoing forum for calibration of policy. I have a hard time seeing that policy shaped without the UK wanting to be at the table.”

British Influence’s director, Peter Wilding, said: “Eurosceptics who peddle the myth that Norway is the best [model] for a non-EU Britain are deceiving the British public. They say leaving leads to more democracy and security. This is nonsense.

“We now have the Norwegian Europe minister himself telling us to get a grip, get real and get involved in shaping Europe. Little England cannot be an option,” Wilding said.