Ms Gabbard added that she was also seeking legal advice over whether the UK had breached an agreement between it and the US not to demand data belonging to each other’s citizens.

In response to the Home Office notice, last week Apple pulled its top level privacy tool, Advanced Data Protection, from the UK market.

Advanced Data Protection, external (ADP) means only account holders can view items such as photos or documents they have stored online through a process known as end-to-end encryption.

Apple would have to break its encryption systems in order to comply with the UK government demand, as currently it cannot see data protected in this way so would be unable to share it with law enforcement. This is something it says it will never do.

Apple’s UK users’ data remains encrypted in the UK but at a level which means it can be accessed by the tech giant if served with a warrant.

The letter to Senator Ron Whyden and Representative Andy Biggs which has now been published online, Tulsi Gabbard said she first read about the notice in the media and had not been informed beforehand by either the UK or by Apple.

Apple did not comment. The Home Office has been contacted by the BBC.