Thank you for your answers so far.
My meter has to be changed, the service head and tails are obsolete so that indicates age of electrical installation. The meter is being moved to the outside wall and I have to give my KVA to installer. Electricity was installed long before central heating and electric showers were available. If the current KVA is not sufficient can I simply tell them whatever I need and what would the optimum for multiple showers and appliances be? Is 19.5 already suggested sufficient?