Google is secretly reaping millions of money from vulnerable people, seeking treatment for addictive diseases, by charging advertisers secretly working for private clinics' in Britain, a media report said on Sunday.

The internet giant charges the middlemen -- known as referral agents -- as much as 200 pounds each time someone visits their website via search page advertisements at the top of a Google page, an investigation by The Sunday Times has revealed.

The referral agents advertise themselves as free advice helplines but receive as much as 20,000 pounds commission monthly each time a new patient is referred to private rehabilitation clinics, the report said.

"The level of payments for these referral agents via promoted links cannot be justified in my view especially as those desperate to tackle their addictions are unknowingly picking up the bill," Sarah Wollaston, the Conservative MP, who chairs the health select committee, was quoted as telling The Sunday Times. 

She also reportedly called on Google, which made 59 billion pounds from advertising in 2016, to stop selling advertisements to referral agents.

Google refuses to take advertisement from referral agents in the US, where the practice is illegal, but in Britain, it spurs by creating a bidding war between referral agencies who want their advertisements appear at the top of the Google search page, said the report.

However, the tech giant, in a statement on Sunday printed in the Sun, said that they have decided to "extend" the practice of banning referral agents to Britain. 

The Sunday Times report meanwhile said that huge commissions taken by these agents have been blamed for significantly increasing the cost of private care for people suffering from addictions. 

The referral agents are "parasites targeting sick people at the most desperate time of their lives", said Dominic McCann, development director at the Castle Craig addiction hospital in Scotland. 

The illegal practice was discovered by undercover reporters, who filmed two meetings held in 2017 between Britain's leading referral agency executives with Google and the rehabilitation clinics.

The reporters were posing as executives from a new treatment centre that was to be opened in Gloucestershire.

One business owner was reported to have said he was spending 350,000 pounds on Google advertising, to ensure addicts visited his helpline first, the daily revealed.

The Sun quoted a Google spokesperson as saying that they "work to help healthcare providers -- from doctors to hospitals and treatment centres -- get online and connect with people who need their help".

"Substance abuse is a growing crisis and has led to deceptive practices by intermediaries that we need to better understand.

"In the US, we restricted ads entirely in this category and we have decided to extend this to the UK as we consult with local experts to update our policy and find a better way to connect those that need help with the treatment they need," the spokesperson said.