The retailer said this had already started to make a difference with "customers noticing improved availability both instore and online". Asda is the UK's third largest supermarket, behind Sainsbury's and Tesco. Lidl has been growing its share of the UK grocery market (Andrew Matthews/PA) However, it faces the prospect of being overtaken by German chain Aldi which is the fourth biggest supermarket in terms of grocery market share. Aldi held a 10.4% market share in the three months to November 3, unchanged from the same period last year. Meanwhile, Lidl has been growing its overall share of the UK market as the low-cost grocer continues to open new stores and tap into demand among shoppers for cheaper deals. Its market share rose to 7.7% in the latest period, from 7.4% the same time last year, with consumer spending surging by 7.4%. Lidl has said it is opening 10 new shops in the UK before Christmas and has set its sights on opening "hundreds" more in the future.