CBD is legal in the UK as long as it does not contain more than trace amounts (more than 0.2%) of THC, which is a controlled substance under the Misuse of Drugs Act 1971. CBD is legal in the UK provided it has been derived from an industrial hemp strain that is EU-approved or comes from outside the EU. Please check the laws in other countries before traveling.
Basically, the law will vary from country to country, and it depends on whether the CBD comes from hemp or marijuana.