John Lewis delivered its best-ever performance last week, with sales up 15% to £142m driven by online sales on Mega Monday on December 3.

For the week to December 8, John Lewis recorded an online sales surge up 46%. Shop sales also advanced, which John Lewis said confirms the success of its omnichannel strategy.

John Lewis retail services director Barry Matheson said: “To have achieved these new sales records, particularly in a market which is still economically challenging, shows the extent to which customers trust John Lewis to deliver the perfect Christmas. Doing everything we can to reward customers’ faith in us with outstanding service and product availability must be the focus for the final two weeks.”

Electrical and home technology was the top performer across stores and online with customers snapping up tablets and headphones. John Lewis said the hearmuffs were particularly popular.

Colder weather pushed up sales of outerwear and cashmere, and sales accessories such as gloves and scarves also lifted. The Home category delivered a record week ahead of the usual peak for gifting, which John Lewis said “bodes well for the week ahead”.

Stores in Scotland and the north of England performed particularly well despite the snowfall early in the week. The Swindon store came top of the sales league but John Lewis said the stand-out performance came from Glasgow.

Waitrose, John Lewis’ sister company, delivered a 6.8% sales jump, excluding petrol to £125.9m last week.

Waitrose said its stores were getting busier as Christmas nears with the number of transactions up 1.6% on the previous week. Customers were also buying more with volume up 2.2% on the previous week and 8% up on last year.

The supermarket’s online business saw sales rocket 45.3% and said it is seeing an “increasingly digital influence” with orders via mobile phones up 30% week on week and 16% of orders made using a tablet. Click-and-collect sales surged 32%.

With the Christmas party season here, Waitrose said sales of hand-picked mistletoe had soared 45%.

Sales of Heston Blumenthal’s Hidden Sauce Figgy Pudding, which launched last week, were “phenomenal” and the £14.99 pudding has been listed on eBay for more than £100.

Waitrose said seasonal confectionery sales rocketed 85% last week but the Belgian Box of Chocolates has been the biggest hit as parents buy end-of-term gifts for children to give to their teachers. Selection boxes are also up 74% as shoppers spread the cost of Christmas rather than leaving it to the last minute.

Advent calendar sales almost doubled against last year.