Upmarket grocer Waitrose has become the third supermarket to deliver a profit warning this year, after Tesco and Morrisons, as it declared results would be under par.

The latest figures show Aldi is poised to overtake Waitrose as the discounters eat up market share from the most established grocers in the UK as the big four becomes the big seven.

“We are in a period of unprecedented investment and this will have an impact on the profit we report next month”, said managing director Mark Price.

Price said it was investing in online, opening new shops and improving existing ones and will invest in price matching and promotions and would offer money off butter and milk for myWaitrose card members. This follows its free coffee and newspaper offer for card holders.

Waitrose‘s sales have slumped dramatically in recent weeks as it battled against tough comparatives last year. For the week to 26 July sales rose 6.7 per cent up from last year. Price forecast a 4.5 per cent sales rise next month.

He concluded: “We are investing to enable us to compete effectively in this very tough market and to build a strong business for the future.”