One of Britain's biggest health chains is selling illegal cannabis oil, The Mail on Sunday can reveal.

High-street favourite Holland & Barrett stocks a brand of oil that contains more than four times the legal limit of tetrahydrocannabinol, or THC, the psychoactive ingredient in cannabis.

Manufactured in Holland, Jacob Hooy oil is reportedly the best-selling cannabidiol, or CBD oil, product in Britain.

CBD products have surged in popularity and are now taken by more than six million Britons, attracted by claims that they help with conditions such as skin complaints, depression and insomnia.

On its website, Holland & Barrett, which has 800 stores across Britain, says the oil is 'non-psychoactive and the content of THC is tested on every batch to meet specification requirements of less than 0.05 per cent'.

On offer: A Holland & Barrett advert promoting its Buy One Get One Half Price deal for the CBD oil (left). Manufactured in Holland, Jacob Hooy oil is reportedly the best-selling cannabidiol, or CBD oil, product in Britain

The oligarch owner building a VERY fancy joint Mikhail Fridman Holland & Barrett's status as Britain's biggest health-food retailer was underlined when it was bought for £1.8 billion in 2017 by a Russian oligarch. Mikhail Fridman, who was ranked tenth on The Sunday Times Rich List last year with an estimated fortune of £10.9 billion, has made his home in Highgate, North London, where he is restoring Athlone House, a 19th Century mansion modelled on the Palace of Versailles. The 55-year-old grew up in the Ukrainian city of Lviv where he ran a student disco called Strawberry Fields and started a window-washing business. In 2003, he struck a deal with BP that formed his company TNK-BP, before creating Alfa-Group, one of Russia's largest multinational conglomerates. His North London mansion Mr Fridman, a divorced father-of-four, plans to leave his fortune to charity and has denied reports of links to the Kremlin. Holland & Barrett was established in 1870 by Major William Holland and Alfred Slapps Barrett in Bishop's Stortford, Hertfordshire, as a grocery and clothing store. The company now has 1,300 shops in 16 countries, including China, the Netherlands, India and Saudi Arabia. It faced criticism in 2012 for employing about 1,000 unpaid people through a government jobs programme. Advertisement

But the Jacob Hooy website says a 10ml bottle of its CBD oil contains 4.4 milligrams of THC. Under the Misuse of Drugs Regulations 2001, the legal limit of THC in any one product is 1mg.

Last night, Holland & Barrett, which sells the oil for £19.99 but is offering a Buy One, Get One For Half Price deal on its website, said it was satisfied that it was 'lawfully marketing these products'.

This newspaper has seen results from tests on a bottle of Jacob Hooy CBD bought from a branch of Holland & Barrett that showed levels of 12.4mg of THC – more than 12 times the legal limit.

The tests were conducted by Fera Science, a laboratory part-owned by the Department for Environment, Food and Rural Affairs. Fera Science works for several Government departments.

Analysis of 31 brands of CBD oil sold in stores and online found ten had THC levels above the legal limit, including one with almost 24mg of THC.

Experts say levels above 10mg can have an adverse effect on cognitive functions.

The revelations will reignite concerns about the safety of products sold in the ever-growing and lucrative CBD market and the ability of regulators to enforce rules.

The CBD industry is overseen by a variety of different Government departments, but critics say this has caused confusion.

The Food Standards Agency (FSA) is the main regulator, but the Home Office is responsible if products contain controlled substances such as THC.

Another watchdog, the Medicines and Healthcare products Regulatory Agency, can intervene if CBD products make medicinal claims.

Manufacturers of CBD products are required by the FSA to prove they are safe.

However, the FSA last night admitted that no CBD products in the UK market have been authorised but declined to say why, as a result, it was not pulling products off the shelves.

Tory MP Craig MacKinlay, the chairman of an all-party parliamentary group exploring the dangers of cannabis, said: 'A limit has been set for a reason and the thought that big, respected health food companies are exceeding these limits is not only a worry, it's making our entire cannabis policy a laughing stock.'

Rebecca Sudworth, director of policy at the FSA, said: 'The FSA has persistently made clear to the CBD industry that they need to apply for authorisation.

'If we don't see compliance soon we will take further action. If any evidence is found to suggest CBD is harmful, it will be removed from shelves immediately.'

Holland & Barrett said the CBD oil was sold as a food supplement and was ‘clearly not designed for administration of controlled cannabinoids as evidenced by its packaging and labelling’.

A spokesman said ‘negligible quantities’ of THC in the oil was ‘due to the technical difficulty in obtaining pure CBD’ but all steps were taken to minimise the THC levels. In any event, it said the THC would have no adverse effect on consumers.

Before the product went on sale in 2016, the firm said it had consulted with the Home Office and lawyers over current legislation and that ‘based on our due diligence we believe that we are lawfully marketing these products, which are also lawfully marketed elsewhere in the EU with similar levels of THC’.