As the tax fiasco continues, we might ask what is to be done to prevent this in future.
I am not surprised amounts of tax were miscalculated. I personally worked on a project to encode a corporate tax return for electronic submission when we found the rules were incompatible. It wasn’t possible to submit a valid return. HMRC discovered this and adjusted the rules only because our electronic testing revealed the problem.
To put it another way, the tax rules were so complex that returns could not be correctly checked manually.
There is a simple solution, albeit not an easy one: massive tax simplification. I wish the Office of Tax Simplification every success!