Article 196 of the VAT Directive requires the reverse charge mechanism on all services subject to the B2B rule introduced in art. 44 of the same Directive. The B2B rule locates the transaction where the business customer is located. In case the customer is a private individual, B2C rules locate the transaction where the supplier is located.
According to the general B2B rule, any business not established in UK supplying services to a UK based customer will not charge any VAT and the transaction will be reverse charged by the customer.
There are however a number of exceptions to this rule. Where these exceptions apply, reverse charge is still applicable in UK:
More information on the general B2B rule is available in the online information published by HMRC.