LONDON (Reuters Life!) - The number of British adults signing up to social networking sites such as Facebook and MySpace has almost doubled in the last two years, according to new research from the country's communications watchdog.

Ofcom said its research reveals that 38 percent of British internet users now have a social networking site profile -- up from 22 percent in 2007.

At the same time, people are also becoming more cautious about sharing their personal information online, Ofcom said.

Three quarters of those with a social networking profile now say that it can only be seen by family and friends -- up from 48 percent in 2007.

Millions of Britons are also now banking, shopping and paying bills online, but one in five (21 percent) would never enter their credit card details online, and nearly a quarter (23 percent) say they would never enter their mobile phone number.

Those who are more confident using the internet are more likely to be happy to provide personal information online, while older people are less likely, Ofcom said in its UK Adults' Media Literacy interim report.

The report also reveals a considerable growth in household take-up of the internet among adults over 65 (41 percent vs. 26 percent) and those in low income households (51 percent vs. 35 percent).

There are also some gender differences in what the internet is regularly used for.

Men are more likely than women to use the web for news, while women are more likely to use the internet for social networking, Ofcom said.

One in three adults who use the internet (29 percent) are watching online or downloading TV programmes or films. Of those, adults aged 25-34 are more likely to watch TV online or download programmes and films and almost all are doing so through television broadcasters' websites.

More adults believe that file-sharing through downloading shared copies of copyright music and films should be illegal (42 percent) than believe it should not be illegal (33 percent), and 25 percent are unsure. Young people aged 16-24 are more likely to say that such content should not be illegal (55 percent).

(Reporting by Paul Casciato; editing by Steve Addison)