The adapter is needed, as the sockets in the UK are three-phase

If there is no own adapter, usually it can be obtained (for an additional fee, of course) at the reception desk of the hotel. However, often there are hotels without adapters to the European outlet at the reception, and then it is better to attend to this issue immediately at the airport, or later, looking for an adapter in "computer" shops and souvenir shops from the "all for tourists" series. Their cost in stores is about 1 - 1, 5 GBP.

However, you can protect yourself from surprises on trips, in advance of purchasing a universal adapter that can be used for almost all types of outlets on the globe. If you plan to travel a lot, it will be a really good acquisition.