Electric shower heating water versus hot water from tank? Which is cheaper

[Gardenista]

I have a house with a 6 year old valiant eco tec 418 gas condensing boiler. the gas central heating runs off this. Installed by previous owner.

There is an fashioned hot water tank - but the survery when I bought the house said immersion heater back up was broken when I bought the house so it's definitely running off the gas boiler.

The main bathroom is an electric shower ( heats the water from cold- a cheap one cost about £100 when I replaced like for like).

Would it be cheaper to

1. shower using the electric shower which heats up the cold water (it's a cheap shower - cost about £100 2 years ago ) and turn off the hot water over winter - I use a dishwasher and washing machine with cold feed and can wash my hands in cold water
2. leave the hot water on and shower from mains hot water in the guest bathroom which has this option (and an electric shower option)

I haven't had a smart meter installed so no idea of the usage but I m with British gas for electricity and gas

Thanks for any advice - should get a smart meter I suppose as well..

Gas is much cheaper as fuel than electricity so use it from the tank, if you are sure the boiler is heating it.