The cost of an average Christmas dinner has surged 6.5% on last year, pushed up by hefty price rises on potatoes, cauliflower, carrots and parsnips.

UK shoppers will pay £32.57 for a festive meal for four, according to retail analysts at Kantar, spurred by a 16.3% jump in potato prices and a near 15% rise in the cost of carrots.

All elements in the meal rose in price except sparkling wine, which remained level on last year with the most expensive item, turkey, up 8.5%. The overall cost of a Christmas dinner rose by almost three times the pace of wider grocery inflation.

Grocery prices stepped up 2.6% in the four weeks to 1 December, up from 2.3% a month before, according to Kantar. Prices rose fastest on household essentials such as toothbrushes and chilled juices, while they fell on items such as dog food and toilet roll.

Spending on groceries to take home rose just 2.5% in the 12 weeks to 1 December – just behind inflation in the final month of that period – indicating that shoppers are still cautious about putting more items in their baskets and searching for ways to save.

Sales of discounted items accounted for 30% of the total in November, the highest level since last Christmas, driven by the use of loyalty scheme price cuts.

Fraser McKevitt, the head of retail and consumer insight at Kantar, said: “Shoppers are grabbing the chance to spend that little bit more than usual on Christmas specials, and champagne, wine and spirits saw the biggest levels of buying on deal.”

However, many households may find that overall festive spending may not be as expensive as the data indicate as most big supermarkets have offered hefty discounts on vegetables in the final week before Christmas.

Despite inflation on costs, the Aldi chain announced on Monday that it would be offering bags of vegetables, including potatoes, for 15p and several other supermarkets are expected to follow suit.

Growers have criticised the Christmas vegetable price war, warning that they are “already under the cosh”.

Meanwhile, Kantar said grocery sales at the upmarket food retailer Marks & Spencer had risen 10.4% in the 12 weeks to 1 December, putting it well ahead of the rest of the market, which was led by Lidl, where sales rose 6.6%.

Kantar said nearly a third of households had bought at least some groceries for eating at home from M&S during the period.

In contrast, struggling supermarket Asda continues to lose market share as its sales sank 5.6% – the only one of the top seven grocers booking a decline. Tesco’s sales rose 5.2% taking its market share to 28.1% – the highest level since December 2017.