Retailers have slashed prices further as they pin their hopes on a bumper trading day as shoppers head out for one of the biggest spending days before Christmas.

Topshop and Miss Selfridge have increased their discounts to up to 60%, from 40% and 50% respectively earlier in the week. Jigsaw, Peacocks and House of Fraser have increased their price cuts to 50%, matching Debenhams, Hobbs and Oasis which deepened their discounts earlier in the week.

Marks & Spencer has added knitwear, its key seasonal category, to its price-cutting promotions with discounts of 40%, as well as a half-price on beauty gifts.

Average price cuts were expected to top 50% by Christmas Eve for the first time, according to the advisory firm Deloitte, which analysed more than 800,000 online and in-store products. It said retailers were being forced to cut prices as they battled discount fatigue after the Black Friday promotional period in November. Lacklustre consumer confidence because of uncertainty about Brexit and the 12 December general election was also a factor, Deloitte said.

Last-minute present buyers are expected to spend £1.7bn on what has become to be known as Super Saturday, according to the Centre for Retail Research (CRR) and the website VoucherCodes, up from £1.63bn last year. The CRR predicts the vast majority of the sales growth will go to online retailers that are now able to deliver right up until Christmas Eve.

Orders for home delivery before Christmas can be made up until lunchtime on Christmas Eve at Argos, 6pm on Monday at M& S, 8pm on Sunday at John Lewis and 10pm on Sunday at Next. On Friday, John Lewis extended the deadline for online orders that can be collected in store before Christmas until 8pm on 23 December.

Retailers are trying to secure late orders amid a nail-biting end to the biggest shopping period of the year as shoppers hold out for last minute bargains.

Sales at established bricks and mortar stores fell by 2.9% year-on-year in the week to 16 December, according to the latest BDO survey which tracks sales at mid-sized stores. Overall sales were virtually flat as online sales rose nearly 6%. Fashion was by far the worst performer, down nearly 4% overall and more than 5% in stores.

Patrick O’Brien, of the industry analysis firm GlobalData, said shoppers had completed less of their Christmas list than usual for this time in December.

He said retailers would now struggle to make up for lacklustre sales in November and early December as shoppers have left their present, food and party outfit buying later than ever.

“There could be a release of spend but whether it comes or not is up in the air,” O’Brien said. He added that the weekend should bring strong trading but the last-minute rush could be badly affected by poor weather. “It’s not going to be turned around into a bumper Christmas no matter how Super Saturday is,” O’Brien said.

Westfield, the owner of two busy London shopping malls, said it expected this weekend to be similar to last year when a record 1.2 million people visited over Super Saturday and the following Sunday.

Myf Ryan, the group brand director for Unibail-Rodamco-Westfield, said: “This year we’re expecting a similar number of people through the doors, either ahead of returning to work for the final two days before Christmas or before taking holiday to visit family and friends further afield. We’re also anticipating a significant surge in overseas visitors looking to make the most of the shopping, dining and entertainment on offer at both our London centres.”