Tantric massage as a commercial massage servcies:

Commercial erotic and sexual massages are provided by independent providers who may be prostitutes. These providers may or may not know about tantric masages.Their broader sexual services include handjobs, oral sexual services, or sexual intercourse. The term tantric massages are also used by commercial sexual massage services to legitimate their services in certain jurisdictions. Commercial sexual massages also offer a ‘happy ending ‘by the introduction of a handjob after their massage sessions. If you search enough then you can always find places where the practice of traditional tantra is followed in your town.

UK sex law:

Massages & tantric massages is legal in UK.

According to UK law:

In the United Kingdom, prostitution itself (the exchange of sexual services for money) is legal, but a number of related activities, including soliciting in a public place, kerb crawling, owning or managing a brothel, pimping and pandering, are crimes.

Read more about: Sex work in the UK: Just what would decriminalising prostitution mean?

Please note: It is illegal to buy sex from a person younger than 18, although the age of consent for non-commercial sex is 16.