Its own figures showed that, in 2015, Apple released data on users' devices to US authorities 80% of the time, compared to 55% when it came to the UK.

That compared to a global average of nearly 60%, Apple's data showed.

A security expert said it was "deeply frustrating" for law enforcement agencies.

Apple released its latest transparency report on Monday to complement previous releases going back as far as 2013.

It published the numbers of device requests it received - those from law enforcement for contact information and other data.

Separately, it released data on account requests - those from government agencies for account details, including iTunes and iCloud account information.

Data release

The BBC's analysis has revealed that, similar to in 2015, the UK was below the global average and the US above it for both types of request in each of the previous years for which there were comparable data.

Among the five countries that regularly submitted a large number of device requests - more than 2,000 per year - the US was the only country to consistently receive Apple customer information a greater-than-average proportion of the time. Singapore was also below the average in each of the three years.

Apple's figures showed that, on average, it was unable to release data for 33% of account requests from across the world in 2015. In the US, the rate was 18% and, in the UK, 40%. A similar picture emerged in 2014. A comparison of account requests in 2013 was not possible because Apple did not release exact figures for the US for that year.

The US and the UK were the only countries to make more than 300 account requests per year.

The consistently lower proportion of successful requests from the UK could be because Britain is seen as "less protective of personal privacy" than the US, said Prof Alan Woodward of the University of Surrey.

The security expert, who advises Europol and who has also advised GCHQ in the past, said: "Whatever the reason, it is a deeply frustrating situation for law enforcement agencies."

Despite Apple's presence in many countries outside the US, he added that it may also feel less duty bound to comply with requests from foreign governments.

'Government abuse'

According to Apple's report, the majority of device requests were in cases of lost or stolen phones and the BBC understands that some of the differences between countries were dependent on the differing approaches of national police forces towards phone theft.

The BBC also understands that some of the unsuccessful account requests were down to the company not holding any information, rather than resisting law enforcement efforts.

The firm declined to comment when contacted by the BBC.

On Monday, Blackberry's chief executive John Chen said the firm would comply with law enforcement but would prevent "government abuse of invading citizen's privacy".

He spoke in response to reports that Canadian police could intercept and read encrypted messages sent using Blackberry phones. Mr Chen said the firm "stood by [its] lawful access principles".

(BBC)