Mark Price, the self-styled “chubby” grocer, has always enjoyed having a light-hearted dig at the opposition. Yesterday was no different as the Waitrose managing director said the chain's new convenience store format would win hands down in a battle with Simply Food.

Sir Stuart Rose, the Marks & Spencer executive chairman, will no doubt have bigger things to worry about today as he reports second-quarter sales. But the Waitrose move into convenience retailing is another irritation he could do without.

Unlike M&S, Waitrose - a business run by the privately owned John Lewis Partnership - can plan for the long-term and not be unduly worried about how the investment in rolling out a new concept during a downturn will affect profits.

There is no doubt that the convenience market is one where Waitrose needs to be: nearly £1 in every £5 spent in the grocery sector is now taken by a convenience store, be it Tesco Express or Costcutter.

Separately, Waitrose knows that if it is to expand across Britain it must develop new formats. The business still has fewer than 200 supermarkets and only 5 per cent of the grocery market. Rather than waiting years to develop land for a superstore, it can now target smaller units that are far more readily available.

Industry experts will question whether the concept can be that successful in the current climate. The emphasis on bringing grocers to the high street could also upset the independents that are already there.

Yet Waitrose is gradually building scale and its rivals will be watching over their shoulders.

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