(Sharecast News) - Sales growth across the UK's grocery sector slowed over the last month, industry data showed on Wednesday, as shopping habits returned to normal after the long summer break.

According to data from research firm NIQ, total till sales growth was 4% in the four weeks ending 7 September, down from the 5.5% rise seen in the previous month.

Within that, online sales of fast-moving consumer goods jumped 6.1%, outperforming bricks and mortar sales, which rose by just 1.8%.

Sales for general merchandising fell 4.5%, as seasonal ranges changed, but fresh food saw stronger gains, including an 8.1% jump in produce.

Mike Watkins, UK head of retailer and business insight at NIQ, said: "September is closely tied to a change in how we shop following 'back to school', so retailers typically reinvigorate marketing efforts as customer refocus on new routines as we go from summer to autumn."

NIQ added that the cooler weather was also likely to have weighed on sales.

Among individual retailers, over the last 12 weeks online-only Ocado remained the fastest growing grocer, with sales up 15.4% year-on-year.

That was followed by Ocado's partner, Marks & Spencer, with sales growing 12.4%.

Tesco remained the market's biggest operator, however, with a market share of 26.4%, followed by J Sainsbury at 14.7% and Asda at 11.8%, which saw sales fell 5.5% year-on-year. In contrast, Ocado has a market share of 1.7% and M&S 3.7%.

Among the discounters, Aldi's market share was 10.3% following just a 0.4% uptick in sales, while Lidl's 7.3% share benefited from an 11.3% spike in sales.