@nprofile1q... That's usually my strategy. If you tell them about non-taxable things, they don't tax you on them. If you think they're not taxable and you're wrong, you pay a bit of tax. If you don't tell them and you're wrong, you have a much bigger liability.
They did telephone me one year because I made an error, which was frustrating because they could have pre-filled the form with the things they knew, but it turned out that the error (typo copying things) meant I claimed more income than I had, so I ended up owing less tax.