If your gas boiler were replaced with a heat pump with an average COP of 4 it would only require around 4,000kWh of electricity to provide the same amount of heating.

Electric cars are similarly 3-4x more efficient than petrol cars on a kWh of fuel basis.

So while we should expect increased electricity demand as transport and heating are electrified, the increase in electricity usage will be far less than the decrease in kWh of fuel.