Voyant

https://www.planwithvoyant.co.uk/content/en_GB/index.html

Unfortunately the cheapest sort of access to this product is around £120/yr via an advisor sponsored subscription, but the insights they provide are nothing short of comprehensive

I pay it, but it is pricey for something you might want to look at just once or twice a year.

A freely accessible alternative is called Timeline (https://www.timeline.co/, sign up as an advisor and add yourself as a client), but it's nowhere near as comprehensive at calculating all your tax burdens and optimizing things etc.

There's a fair amount of tactics in working over the tax system to achieve better outcomes.