''Experts had previously assumed that people who breached gagging orders on Twitter were protected from legal reprisals because the website is outside the jurisdiction of British courts.
The admission came after Dominic Grieve, the Attorney General, warned earlier this week that people who breached injunctions online were in for a "rude shock".
''He said: "It is quite clear, and has been clear for some time in a number of different spheres, that the enforceability of court orders and injunctions when the internet exists into which information can be rapidly posted, that presents a challenge.
"But that doesn't necessarily mean that the right course of action is to abandon any attempt at preventing people from putting out information which may in some circumstances be enormously damaging to vulnerable people or indeed, in some cases, be the peddling of lies."
''Ryan Giggs, the Premiership footballer, last week started legal proceedings against Twitter and "persons unknown" after more than 70,000 users revealed that he had obtained an injunction to hide an extra-marital affair.
On Monday John Hemming, the back-bench Liberal Democrat MP, used parliamentary privilege to identify Giggs in Parliament.
The admission by Twitter, however, could encourage legal action by a number of celebrities who have been named on the website as having obtained injunctions to hide alleged affairs.
Tony Wang, Twitter’s head of European operations, said yesterday the website would notify users in advance so they could fight the application in the court before Twitter handed over the information.''