German discount retailer Aldi has leapfrogged Waitrose to become Britain's sixth-largest supermarket chain.According to data released on Wednesday by Kantar Worldpanel, Aldi sales rose 16.8% in the three months to 29 March, taking the group's market share to 5.3%, 0.2%% more than John Lewis Partnership-owned Waitrose.Waitrose's sales climbed 2.9% but Aldi was the best performer in the market, which saw grocery prices fall 2%, while fellow German retailer Lidl also reported strong growth, as sales jumped 12.1%."The changing structure of Britain's supermarket landscape is illustrated by two facts," said Fraser McKevitt, head of retail and consumer insight at Kantar Worldpanel."Aldi and Lidl now command a combined 9.0% share of the market. "In 2012 the same two retailers only accounted for 5.4% of grocery sales, while the 72.8% share taken by the biggest four retailers is now at the lowest level in a decade."