It depends on the type of consumer and whether they are likely to pay the ‘full price or not’ but generally a retailer selling to the public is required to show the price inclusive of any taxes etc that the majority of customers will be paying.
The most relevant legislation is probably ‘The Price Marking Order 2004’ https://www.legislation.gov.uk/uksi/2004/102/contents/made
this may also help which is a recent discussion on the Advertising Standard Authority Code of Practice which also states that prices should be displayed inclusive in retail situations:https://www.asa.org.uk/news/to-include-or-not-to-include-vat-in-stated-prices.html