In France everything is complicated with a huge number of taxes and rules.
In the UK, if you are employed you don't have to do anything. Income tax and National Insurance are calculated and taken at source automatically. Your other tax is the local Council tax, which is also simple and can be paid automatically.
Helpfully my local council resets your enrollment or automatic payments each year, leading one to forget about them until you get a big nasty letter in the mail.
There is a video of the team presenting how they built the DSL for tax rules in the JetBrains MPS language workbench from the MPS conference.
Case study:
https://resources.jetbrains.com/storage/products/mps/docs/MP...
Video:
I built a tax calculator for English speakers, and highlighting that is next on my todo list. Many people pass up on significant returns, especially parents.
I would guess maybe 20% of people can go through the fully automatic part, but I have no source for that.
Unlike, say, the United States, the French system relies heavily on automation. During tax season, French taxpayers log in to the online tax portal, which is managed by the state. There, taxpayers are presented with online forms, generally pre-filled. If applicable, taxpayers can adjust the forms, e.g. by entering extra deductions or credits. Once the taxpayer is satisfied with the contents of the online form, they send in their return. Behind the scenes, the IR algorithm is run, and taking as input the contents of the forms, returns the final amount of tax owed. The taxpayer is then presented with the result at tax-collection time.