Asda has seen like-for-like sales fall 1% this year, in what it has called one of “its most challenging and changeable periods in history”.

The retailer also saw a drop of 2.6% in like-for-like sales in the 12 weeks to 4 January, including the Christmas period.

Speaking at an event this morning, the supermarket giant outlined some of the steps it had taken as part of its five-year plans, including opening 17 new stores, and unveiling its new format proposition at its Grantham superstores.

It also said it was focused on a long-term plan, including  a £600m investment in “expanding and improving” the Asda store estate.

Andy Clarke, chief executive of Asda, said: “2014 saw an acceleration in the structural shift in the market and, while we saw it brewing and put the right plan in place to address it – delivering solid wins for our business and keeping the ship steady in a turbulent market, the pace and scale of change has exceeded all expectations.

“The first year of our plan was very much about building the foundations –a work-out to limber us up for what is to come in 2015 – by leading the price agenda in a deflationary market. We have a clear plan for sustainable, profitable growth, creating a proposition that gives customers what they want.

“I’m pleased that we can announce our continued investment in the UK with £600m for new and improved stores in 2015. With such a powerful force like Walmart behind us, that fully supports our strategy, we’re in a unique position in a difficult market – a position of great strength.”

The company announced its end-of-year results for the 52 weeks to 31 December.