Britain's decision to leave the European Union could lead to higher cost for groceries as well as to "gaps on food shelves" in supermarkets, with the availability of a number of food items potentially set to shrink.

The warning comes from the British Retail Consortium (BRC), which urged the government to ensure a trade deal is in place by the Brexit deadline of March 2019, or else the supply chains to British supermarkets could be severely disrupted.

"A strong deal on customs is absolutely essential to deliver a fair Brexit for consumers," said Helen Dickinson, chief executive of the BRC.

"Whilst the government has acknowledged the need to avoid a cliff-edge after Brexit day, a customs union in itself won't solve the problem of delays at ports."

Dickinson added that border controls could lead to a shortage of certain food items, highlighting the need for the government to secure a wide-ranging agreement covering key issues such as security, transit, drivers and value added tax.

Over 75% of all food imported in the UK comes from EU countries and HMRC has previously indicated that leaving the bloc without reaching a deal could lead to 180,000 extra firms being drawn into customs declarations for the first time.

While the number in itself might not seem particularly significant, the figure would translate in a sharp increase in the number of annual customs declarations, which would increase almost five-fold from 55 million to 255 million.

As a result, the BRC warned, leaving the EU with no deal could result in lengthy delays at UK ports.

Swiftly reaching a deal with the EU was also crucial to get the "systems ready for March 2019" and ensure any potential disruptions to British supermarkets are minimised, Dickinson added.

"We want to work with the government to develop a system which works for consumers, so that there's no difference in terms of the availability of affordable, quality products when they make purchases or visit stores post-Brexit," she said.

The report also highlighted the need for trade with the Republic of Ireland, whose 310-mile border with Northern Ireland will be the only physical barrier between Britain and the EU after March 2019.

"For the transitional period, a customs union relationship between the UK and EU would help with the implications for trade and the Irish border," the BRC said.

The warnings came as the industry body revealed food prices grew 1.3% year-on-year in August, while the deflation rate for non-food items stood at 1.3%, the slowest on record since April 2013.