This morning on the Today Programme Ed Balls namechecked the blog of Jolyon Maugham a tax specialist QC, he estimated that Labour’s change to the non-dom tax rules would bring in an extra billion. Ed Balls referred to him again later as a “tax expert”:

Just now in the Q & A after his speech Ed Miliband also referred to Jolyon Maugham as an “independent expert” – he’s actually a Labour Party stalwart.

Well other independent experts have taken him to task on Twitter for a basic error, most countries have double taxation treaties (DTCs). If you pay tax in one country on your earnings, you can’t be taxed again in another jurisdiction – the UK has over 100 such treaties. On Twitter Jolyon has conceded “I accept DTCs could have some impact. There’s plainly some uncertainty about the numbers.” When you take this into account the net tax take will be nowhere near the billion claimed…