For a fee of up to £2,000, criminals secretly listen in and, via a hidden earpiece, give the answers to those taking the Life in the UK test.

Such an operation was secretly filmed by a BBC journalist, who was given help to pass.

The test is failed by about one in five would-be British citizens.

The Home Office said it took any cheating "extremely seriously".

A pass in the test, which assesses candidates' knowledge of UK laws, history and society, is usually required as part of the process to secure UK citizenship or indefinite leave to remain.

The number of applications for citizenship made by EU nationals rose by 32% last year and the BBC heard some were paying criminals to cheat the Life in the UK test, as anxiety grows over citizenship rights post-Brexit.

One woman, an EU national, told the BBC she decided to cheat after failing first time around, saying she "felt so much panic" about her situation.

Image caption The gang provided an undercover researcher with a hidden two-way earpiece, linked wirelessly through a Bluetooth connection to a concealed mobile phone with an open line

Over the past year, nearly 150,000 people have sat the test, which consists of 24 multiple-choice questions.

The test, which is taken on a computer and has a pass mark of at least 18 correct answers, is supposed to be held under strict exam conditions.

Administration of the tests is outsourced by the government. There are 36 testing centres in the UK.

BBC researchers were able to access organised cheating when they went undercover at training academies in and around London, where candidates take classes to prepare for the test.

Masoud Abul Raza runs the Ideal Learning Academy in east London.

Masoud Abul Raza has denied cheating, despite being caught on camera

He was filmed telling an undercover researcher that he could guarantee a pass.

"You have to spend nearly £2,000. This is the business, it's completely hidden. But you are getting a result," he said.

Mr Abul Raza and his gang later provided the undercover researcher with a hidden two-way earpiece, linked wirelessly through a Bluetooth connection to a concealed mobile phone with an open line. This meant the gang outside could hear the audio feed of the test questions and provide the answers.

"Everything will be arranged. He will give you the answer," Mr Abul Raza told the undercover journalist.

Tony Smith, the former director general of the UK Border Force, was shown the secretly recorded footage and described it as "clear and blatant cheating by an organised crime gang".

"One would hope that the standards will change significantly so that the public can be assured that people going through this process are genuinely entitled to stay in this country," he said.

The BBC researcher received a pass certificate after being given the correct answers

The Home Office said test centres were required to put in place stringent measures to prevent cheating, including searches of candidates to ensure no electronic devices enter the test room.

"Unannounced visits" are also carried out to audit these processes.

But the BBC's undercover researcher was not searched or told to hand over all electronic devices.

He sat the test, giving the answers provided to him, and within minutes of it ending he had received the pass certificate required to apply for citizenship and a UK passport.

Despite being caught on camera, Mr Abul Raza denied cheating, maintaining he only organises legitimate training.

When confronted, Mr Abul Raza told the BBC he only organised legitimate training

However, he is not the only one profiting from cheating the system.

The BBC heard reports of other training academies doing the same thing, with the same method of cheating having been used at testing centres around the UK.

At the English Language Training Academy (ELTA) in east London, Ashraf Rahman told the BBC's undercover researcher that he had arranged cheating in Birmingham and Manchester, as well as London.

"I've been here for five years and no-one gets caught," he said.

Mr Rahman later denied he arranged cheating, claiming he was just discussing what others did.

ELTA denied cheating took place on its premises and said Mr Rahman was not an employee.