UK supermarkets could soon be banned from offering buy-one-get-one free and other such special deals as these are seen as misleading, making consumers spend more. The ban could be enforced by the Competition and Markets Authority (CMA), the UK consumer regulator and watchdog, after research showed that such deals were "seducing" shoppers to spend an additional £1,000 (€1,287, $1,453) a year.

The watchdog's plans to clamp down on the supermarkets including, Waitrose, Tesco, Sainsbury's and Asda are in the final stages. The companies stand to be accused of unlawful practices in their pricing and promotions policies which end up encouraging shoppers to spend more than what they originally intended to.

The official investigation of the supermarkets follows a "super-complaint", a rarely used legal power being invoked by consumer group Which? that asked for action against companies that had adopted unfair trade practices. A spokesman for the CMA said: "Following the CMA's response to the Which? super-complaint published on 16 July, 2015, we have been undertaking further analysis of the potentially misleading practices identified in our report and establishing our priorities for further action."

Some of the accusations by Which? were that multi-buy offers did not translate to a real saving, price discounts were based on previous prices that were not genuine and that seasonal offers were fake as the higher price on seasonal products were applicable when these were out of season. The CMA clampdown could result in tighter pricing rules for all supermarkets apart from prosecution and huge fines for supermarkets found guilty of offering unlawful deals.

The investigation follows a recent study by the Money Advice Service (MAS), a government-backed body, which revealed that the average spend by shoppers per week was 21% more than what they had planned because of falling prey to the "deals". John Penberthy-Smith, customer director at MAS said: "The problem is that quite often we see a special offer at the supermarket and we don't want to miss out – so we throw it into our trolley without really thinking about whether it is a good deal or whether we actually need it."

However, a spokesman for the British Retail Consortium, which represents supermarkets, argued that the UK supermarkets were "committed to treating their customers fairly and to avoid misleading them in any way".

"Millions of shoppers across the country enjoy the benefits of price promotions and special offers. Recent research has shown that, with the exception of fruit and vegetables, food prices in British supermarkets are on average 7% lower than the eurozone average. In addition, major supermarkets have worked with government and public bodies to make pricing clearer and simpler for customers, such as improving the way that unit price is displayed," according to The Telegraph.