Websites belonging to UK media firms are attracting far more visitors from overseas than from inside Britain, new research has found.

Industry analysts have predicted that online advertising spend worldwide will overtake radio advertising next year – but the new findings from internet market analyst firm comScore suggest advertisers will need to devise strategies that take account of internationalised readerships.

The comScore research found that visitors from outside the UK outnumbered domestic readers on the BBC, Guardian, Telegraph, Times, Independent, Daily Mail, Mirror and Financial Times websites.

The Financial Times website, ft.com, has an overwhelmingly overseas audience, with 85% of visitors coming from outside the UK.

Only TV stations Five.TV, ITV, BSkyB and Channel 4 had a larger UK than international audience, the research for April this year found.

Bob Ivins, managing director of comScore Europe said: "It is critical for publishers and advertisers to understand their global franchise – not just their UK audience."

The BBC had the largest number of UK visitors of the media websites surveyed by comScore, with 17.9 million unique visitors in April – but this was just 39% of its traffic, with total worldwide visitors amounting to 46.4 million.

The Guardian's website had the highest visitor numbers among the sites run by UK newspapers, with 3.2 million UK visitors and 7.7 million from overseas – 58% of the total. The Financial Times had slightly more than 2 million visitors from abroad, but just 305,000 from the UK.