Erna Solberg’s concern comes as Brexit Secretary David Davis announced the UK is considering becoming members of EFTA temporarily, in order for Britain to remain in the EU’s common market, the European Economic Area (EEA).
Ms Solberg, whose poll results have increased ahead of the Norway election on the September 11, is concerned about what impact the UK joining EFTA would have on smaller countries in the organisation.
Ms Solberg told Norwegian tabloid Verdens Gang: “It would weaken EFTA as an instrument for small countries.
“The UK is a much larger country that has other interests than the small countries that are already members of EFTA.”
Norway is a key player in EFTA, which Iceland, Switzerland and Lichtenstein are also part of.

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The UK was was a co-founder of EFTA in 1960 but ceased being a member upon joining the European Economic Community.
Ms Solberg has cast doubt on whether the UK could join EFTA easily, even temporarily.
She said: “If so, there would be a long transitional period, because it takes a long time to get a final agreement in place with the EU.”
Ms Solberg also told Reuters it would be challenging and costly for Britain to rejoin the trade bloc, because of some of the obligations Theresa May’s Government objects to.
She said: “I believe, in consideration to Norwegian agriculture in particular, that we need to be sceptical.
“Their interests are opposite to ours: They are net exporters of agricultural products. We are net importers. It would be difficult to reach an agreement that would benefit both countries.”
When asked whether Norway would have the opportunity to block the UK from EFTA she said: “There could be a foreign political situation that would put pressure on us, but it is too early to say.”