Thanks for that.
The case I'm looking at has total income from all sources smack in the middle of the £2560 band. My own income means I've never had to look at this before. I'll bet many elderly people are paying too much tax due to the complexity of this.
I looked at ITA 2007 s18 briefly and lost the will to live. ITTOIA 2005 Part 4 Chapter 2 looks a little easier to follow.
Once taxable non-savings income (eg earned income) equals £2,560 then no part of any savings income qualifies for the 10% rate (ie the basic rate 20% applies thereto).
So if taxable non-savings income (eg earned income and dividends less allowances) total £1000 then the first £1560 of "savings income" (as defined in ITTOIA 2005 Part 4 Chapter 2) should be taxed at 10%.
Am I right in thinking that most people in that position will have had £1560 taxed at 20% at source so might be due a refund?