The most powerful shower it's possible to have on a normal electrical circuit (single phase). 12.5kw of power, you can expect a good flow of hot water. 
These showers will not only need to be installed by a qualified electrician, you will absolutely need to check with them BEFORE PURCHASING that your power supply can work with a 12.5kw shower. 
They will be able to advise. These are NOT plug in showers, the 3kw plug in ones are available but are much less powerful as they have to go through a plug socket. They're the 'Micro-E' ones here: https://www.hipposhowers.co.uk/product-page/new-micro-e
 
Digital display, touch screen controls. All the awesomeness you've come to expect from Hippo in a sparkly modern electric version. Please note, these are expected in stock by the end of November 2025.