was a long time ago, I know that resulted in no gas in many flats, but as said electric CH and DHW does not really need a boiler as such.
First is the consideration if worth off peak, if so some storage is required, water storage likely best as it self cools slower, but heavy and bulky, so it is where it will fit, and if the premises and stand the weight.
Heat pumps are cheapest to run, but also expensive to install. So unless going for a heat pump, the likely independent convection heaters in each room is way to go.
As to DHW if you want a bath really no option but a storage tank, with a 28 kW gas boiler instant heat it took an age to fill a bath, with a 14 kW boiler it would be cooling down before you have filled it, so for a bath you need a storage tank. If no bath then you can get instant hot water showers and sink units, but likely would be better with small storage tanks around 7 litres, had one in my caravan, it was just 1 kW and because it stored the water could fill a bowl quickly.
But it does not take much calculating to realise 28 kW from a gas boiler is 122 amp, and most houses have no more than 100 amp, many only 60 amp supply, so it is not as simple as just swapping the boiler. Your looking at a 3 phase supply. What regulations have been quoted?