Home Secretary Sajid Javid has announced a major review into the medical use of cannabis.

It comes after a string of high-profile cases of children with severe epilepsy being denied access to the substance to control seizures.

Cannabis is currently a controlled drug classified by the Misuse of Drugs Act 1971.

A follow-up of this law, the Misuse of Drugs Regulations Act 2001, placed it under Schedule 1, the category for substances with no medical use.

It is this schedule that is being considered by the review.

Speaking to MPs, the senior Cabinet minister said that a new panel - to consider applications for special consent for the use of cannabis oil and similar substances - would begin within a few days.

But what is cannabis oil and is it legal? Here's everything you need to know.

What is cannabis oil?

Cannabis oils are extracts from the cannabis plant. The two main active substances in cannabis plants are cannabidiol - also known as CBD - and delta-9 tetrahydrocannabinol, commonly referred to as THC.

The oil extracted from plants contain CBD, which tends to be well-controlled to make it easier for people to calculate doses.

The Home Office says that the oils can contain a maximum THC level of 0.5%, and that it must not be easily separated.

THC is the substance which produces the high recreational cannabis users seek.

Cannabis oil is thought to have medical properties which help to relieve pain and inflammation, as well as reduce anxiety.

In 2016 the nation's medicines regulator, Medicines and Healthcare products Regulatory Agency (MHRA), said that CBD products that were advertised as use for medical reasons needed to be licensed.

Is cannabis oil illegal?

It can be sold legally in Britain if it contains a THC maximum level of 0.5%, if it is higher than this then the product can be confiscated.

What can it be used for?

It can be beneficial for people who suffer from epilepsy, stress, anxiety, depression and lack of sleep. It has also been suggested that it can be used to help alleviate the pain of cancer patience.

Macmillan.org.uk said: "There are side effects of using cannabis oil. Cannabinoids can increase your heart rate, cause dizziness, hallucinations, paranoia and make you feel ‘stoned’. They may also interact with other drugs."

It has also been claimed cannabis oil can treat symptoms of Alzheimer’s Disease, Parkinson’s Disease and MS.