Morrisons has cut the price of more than 500 everyday groceries including beef mince, coffee and biscuits as it battles to climb out of a sales slump.

Industry data shows Morrisons is the worst-performing member of the big four supermarkets amid an exodus to the fast-growing discounters Aldi and Lidl.

Shares in Yorkshire-based Morrisons have fallen by 17% in the last year and it narrowly avoided losing its place in the FTSE 100 in this month’s quarterly review.

Morrisons said the price reductions, which average 15%, were not a gimmick but part of a plan to make products “more affordable and prices stable for customers”. It said hundreds more cuts were scheduled for the coming weeks.

“These price cuts will help customers manage their budgets,” said Andy Atkinson, the commercial director. “We’re cutting the price of hundreds of our customers’ favourite items and are holding them low.”

The reductions are on staples such as a four-pack of baking potatoes, down 15p to 50p, and products from its food manufacturing sites such as British beef mince, now £1.50 for 500g, which the grocer claimed was the best price in the market.

Morrisons had a disappointing Christmas and is due to report its annual results next week. At the start of the year it said it was axing 3,000 middle managers. The plan involves eliminating higher-paid managerial roles while creating 7,000 hourly-paid roles in an effort to improve customer service and reduce gaps on its shelves.

Kantar data for the 12 weeks to 23 February showed sales at Tesco and Asda dipped by 0.8% and 1.2%, while Morrisons sales were 2% lower than the same period last year, pulling its market share down from 10.4% to 10.2%. The figures showed the German chains Lidl and Aldi were continuing to win over British shoppers, with sales up 11.4% and 5.7%.

This week the market leader, Tesco, acknowledged the threat posed by the discounters as it launched its Aldi Price Match campaign. It is price-matching its rival on hundreds of branded and own-label goods as it tries to hang on to shoppers.

The offers include Tesco’s generic “farm” brands, items from the company’s core range, and covers products sold online and in store. Examples include beef mince, some yoghurts, and fresh items such as pre-packed broccoli and avocado.

Tesco said it would be monitoring prices to “give customers peace of mind”. Its chief customer officer, Alessandra Bellini, said the move would mean “budget-savvy customers get Tesco products at Aldi prices on products that matter to them”.