Tesco boss Philip Clarke has quit Britain’s biggest retailer as it is set to miss profit forecasts in what has been described as ‘a disastrous three year reign’.

Clarke, who also came under fire last week from NFU’s Meurig Raymond, is set to leave the company on Octover 1 to be replaced by Unilever executive, Dave Lewis.

The retailer, which once saw significant growth, witnessed a 3.7% fall in like-for-like sales last month as it is squeezed by discount retailers such as Aldi and Lidl.

Despite its £1bn turnaround plan, latest figures from research firm Kantar Worldpanel found that Tesco's market share had fallen to 29% in the 12 weeks to 25 May, down from 30.5% a year earlier.

Clarke, who told delegates at the NFU conference earlier this year that Tesco would seek to support UK agriculture and wished to shorten the supply chain, came under scrutiny from the NFU last week for its lamb imports.

The NFU President commented: Tesco states yesterday that ‘with the large demand for lamb we cannot always guarantee consistent UK stock.’ I find this comment almost as ridiculous as last September’s statement from Tesco that British lamb was ‘not in season at the moment in the UK’. I am angry and disappointed that this comes only 18 months after giving such positive undertakings on its sourcing and supply chains for red meat.

The retailer, which has also been under scrutiny from the public since the horse meat scandal, has had a troublesome year after some of its meat products were contaminated by horse meat but also after it was investigated by the Advertising Standards Agency for its adverts which were claimed to be ‘misleading and appeared to cast doubt over the entire food industry’.

Today, protests took place on the first day of the Royal Welsh show as protestors scrutinised Tesco for its lamb imports and not using British lamb.