Discounters Aldi and Lidl are worth a collective £344 million more than this time last year as a cooler spring slowed supermarket spending against last May's record temperatures, figures show.

The two supermarkets reached a combined record market share of 13.8 per cent over the 12 weeks to May 19 as almost one million more UK households visited Aldi compared with last year and an additional 630,000 shopped at Lidl, Kantar reported.

Their success comes as the grocery market grew by 1.3% compared with the same period last year, when the hottest May on record combined with the royal wedding and FA Cup final resulted in a 2.7% boost for the sector.

While Tesco's overall sales were flat, its performance was the strongest out of the big four during the past 12 weeks.

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Aside from Aldi and Lidl, the Co-op delivered the strongest bricks-and-mortar sales growth of 3.7%.

Gourmet Burger Kitchen (GBK) has seen sales recover rapidly in the early part of this year as it emerged from a dramatic restructuring plan, the brand's parent company said.

The burger restaurant's South African owner, Famous Brands, said on Wednesday that like-for-like sales in the last 12 weeks have risen 8.1%, well ahead of the wider market.

This followed a dip of 4.2% in the 52 weeks to February 24, marking an improvement on the 6.8% decline recorded in the previous year.

But losses before non-operational items widened to £4.6 million.

Sir Martin Sorrell's S4 Capital saw like-for-like revenues jump 41 per cent in the first four months of 2019, the company said ahead of its annual general meeting.

The former WPP boss said his firm saw staff numbers double to 1,300 people as it was buoyed by the acquisitions of MediaMonks and MediaHive.

Shares were up 0.99% at 168p.