"Swedes are really rather self-righteous when it comes to their English skills," said Maria Andersson at translation firm Amesto, which ordered the survey from Novus.
Every other Swede regards their English to be better than average (for a Swede) with only one in ten saying that their abilities are below average.
Amesto commissioned the survey after running into problems with clients who felt they didn't need any help with their Swedish to English translations and others who complained that the professionals' work was not up to scratch.
"We often hear: you can handle the other languages but we'll manage the English," Andersson explained.
"They perhaps think that the content is poor or comment on terminology or grammar, saying 'this doesn't sound good, I wouldn't have put it like that'. This is something we hear very frequently. There is always a discussion when we translate from Swedish to English."
The survey showed that men and Stockholmers were most likely to have a high regard for their own English abilities. Some 24 percent of Stockholm residents consider their English to be "much better" than Swedes in general while 55 percent of men regard themselves "much better" or "better".
"There are a lot of people in Sweden who think that they speak English very well. We read books in English, many have gone to university and read English course literature and we watch American films," Maria Andersson said.
"But we are perhaps not quite as talented as we think. I don't think you or I could write a decent manual for a submarine," she added.
BP chairman Carl-Henric Svanberg caused global outrage a few years back and prompted a brief bout of Swedish linguistic self-reflection when he uttered the words "we care about the small people" while the Gulf of Mexico oil crisis was at its height.
Svanberg was referring to the "average Joe" or "man in the street" but his words led to several language experts to question the self-belief of Swedes in general when it comes to their language abilities.
"It is one of the Swedes' enduring myths – that we speak English as well as we do Swedish. We do not – only a very few Swedes do," said Lars Melin of Stockholm University to Sveriges Television at the time.