Cannabis is not recognised as having any therapeutic value under the law in England and Wales, and a person can commit any of the range of offences including possession and supply. 

However, there is a cannabis-based product - Sativex - which can be legally prescribed and supplied in limited circumstances. 

In 2006 the Home Office licensed Sativex so that:

• Doctors, at their own risk, could privately prescribe,
• Pharmacists could possess and dispense, and
• Named patients with a prescription could possess

In June 2010 the Medicines Healthcare Regulatory products Agency (MHRA) authorised Sativex as an extra treatment for patients with spasticity due to Multiple Sclerosis (MS). Doctors can also prescribe it for other things outside of the authorisation, but this is at their own risk.

Since April 2013 Sativex has been separated from Cannabis - Schedule 4(i)  now applies instead of the old Home Office licence.  However, it is still a Class B  drug and so possession, supply, possession with intent to supply, importation and exportation are all still offences outside of this. Re-supply of prescribed medication (except to a person legally allowed to possess it) is unlawful supply.  Additionally, a person who doesn't disclose, or makes a false statement about, having already been prescribed Sativex to get more supplies from another Doctor will not be legally in possession of any drugs they get as a result of failing to disclose or making a false statement.

Medical Cannabis from outside the UK

Under Article 75 of the Schengen Agreement  the UK allows residents of other EU States which have signed up to this to travel with their prescribed narcotic or psychotropic substances, including Cannabis, into the UK as long as they have a certificate authorising this from their own country. 

This only applies to residents of other Schengen states, and not to UK residents who are prescribed Cannabis in another country.

So, a Dutch resident who is prescribed medical cannabis will be free to come to the UK with their medical cannabis, as long as they have the certificate and aren't coming for more than 30 days.  However, a UK citizen cannot travel to the Netherlands, be prescribed medical cannabis there and legally bring it back into the UK as they are not a resident of the Netherlands. 

UK residents are advised not to travel abroad to bring back drugs that can't be legally supplied in the UK.  Cannabis is still a Class B drug and so anyone bringing it into the UK outside of the Schengen arrangements would be committing importation and possession offences, and risk being arrested and prosecuted.

Even if a UK Doctor prescribes Cannabis to be given by a Dutch pharmacist, the patient would not be able to bring that drug into the UK legally, because this would still be outside of the Schengen arrangements. 

UK citizens are also allowed to travel to other Schengen states with their medication - so someone prescribed Sativex in the UK can legally take it to another county that is signed up to the agreement.