I always find the "how much is a pint of milk/loaf of bread"" questions to senior politicians (or anyone) a bit silly as the price varies so much- a loaf of bread can cost anywhere between around 30p and £1.50, plus more for artisan loaves, for example.
ff, that needn't stop them from answering the question - a wrong answer within a reasonable range is better than just shrugging like BoJo and saying who gives a ****.
Though they probably shouldn't say "£5, but that's because I only eat bread made from the rutubaga of southern Romania".