Boris Johnson’s bid to bring back pounds and ounces will cost taxpayer £2m, Truss warned

Much-ridiculed idea will also confuse shoppers and require lessons in schools, standards watchdog says

Liz Truss is being urged to dump the post-Brexit plan to bring back imperial measures if she wins the race to No 10 – because it will cost at least £2m and bewilder shoppers.

Boris Johnson’s much-ridiculed idea will force traders to fork out on new measuring devices and inspectors to pay for extra training, a standards watchdog is warning.

A poll by the Chartered Trading Standards Institute (CTSI) also found that only half of shoppers were “confident” they could use pounds, ounces and gallons – falling to 30 per cent of under-44s.

John Herriman, the organisation’s chief executive, said: “At a time when we are facing a cost of living crisis, we would question whether this measure is necessary.

“When many of us are thinking about pounds and pence, should we be distracted by discussions about pounds and ounces?”

A “national public education campaign” on TV, radio and online about long-forgotten imperial measures – possibly including school lessons – would probably add millions more to the bill, the CTSI says.

Graham Wynn, assistant director of business regulation at the British Retail Consortium, warned of the “unnecessary complexity for consumers” from the move.

“Currently, the indication of imperial measures is allowed alongside metric ones where that is helpful for customers,” Mr Wynn pointed out.

The plan was unveiled by Mr Johnson to coincide with the Queen’s platinum jubilee in June, as the prime minister hunted for his elusive Brexit “dividend”.

A consultation, to be inherited by the new prime minister on 6 September, also includes a guide to help pubs replace the EU-wide CE marking on pint glasses with the royal crown.

Under EU laws that have applied in Britain for more than 20 years, grocers must display their products in metric measures – with the exception of beer, cider and milk, for which pints can be used.

The government has promised to give grocers the choice to use either system, arguing that imperial measurements are “part of our national identity”.

However, it is exploring whether equivalent metric measurements should also be required – in an apparent admission that shoppers will be left confused otherwise.

In June, the Asda boss and Conservative peer Stuart Rose called the plans “complete and utter nonsense”, saying: “We have got serious problems in the world and we’re now saying ‘let’s go backwards’.

“Does anybody in this country below the age of about 40 know how many ounces there are in a pound?”

The CTSI survey, of 2,016 UK adults, carried out earlier in August, found that:

* Only 23 per cent believed imperial measures would improve their shopping experience, while 26 per cent said they would not and half were not convinced either way.

* More than half of the respondents (56 per cent) had no view on whether they would be more likely to shop from a business that provided imperial measures.

* Only around 30 per cent aged between 16 and 44 said they would be confident applying imperial measures, rising to almost two thirds of those aged 65 and over.