It’s a question often put to politicians in interviews, but this week, Boris Johnson and David Cameron have both shown they have little idea what a pint of milk or a loaf of bread costs.

In an interview on Monday’s edition of Newsnight, London Mayor Boris Johnson was asked by Jeremy Paxman: “Do you even know the cost of a pint of milk?” Johnson replied; “about 80p or something like that?” Paxman said he was wrong and Johnson replied; “I don’t know what a pint of milk cost, so what?” As the interview was based around the rising cost of living, it wasn’t an unreasonable question to be put to the London Mayor.

Clearly failing to notice the coverage that Johnson’s answer had received, prime minister David Cameron was caught out by a similar question soon afterwards during an LBC radio show. When Nick Ferrari asked Cameron: “What does a ‘value sliced white bread loaf’ cost?” he replied, “Well north of a pound”. When told that his guess was double the actual cost, Cameron said that he didn’t actually buy value bread – but made his own in a £100 breadmaker.

This wasn’t the first time that Tory politicians have been caught out. In July last year, agriculture minister Jim Paice was forced to confess that he didn’t know the cost of a pint of milk on Radio 4’s Farming Today programme.

So, does it really matter if ministers don’t know what basic items cost? Many people would think it has little consequence for whether they can run a government. But the fact that they keep getting asked the same questions – and keep getting them wrong – ought to tell us something.