It said UK consumers would face a £682 (€778) jump in their annual grocery bill if they continued to buy the same items. Prices were rising fastest in products such as margarine, milk and dog food.
Kantar said 27% of UK households reported that they are struggling financially - double the proportion it recorded last November.
"Nine in ten of this group say higher food and drink prices are a major concern, second only to energy bills, so it’s clear just how much grocery inflation is hitting people’s wallets and adding to their domestic worries," Fraser McKevitt, Kantar's head of retail and consumer insight, said.
Kantar said grocery sales rose by 5.2% on a value basis in the 12 weeks to 30 October year-on-year – masking a drop in volumes once inflation is accounted for.
Sales of own-label goods, which are generally cheaper than branded goods, jumped 10.3% over the four weeks to 30 October, while sales of branded goods rose 0.4%. Sales of the very cheapest-value own-label ranges soared 42%, as shoppers sought savings.
Discounters Aldi and Lidl were again the fastest growing grocers over the 12 weeks, with sales up 22.7% and 21.5% respectively. Morrisons and Waitrose were the laggards with sales falls of 4.6% and 1.9% respectively.
Kantar noted that fewer people were stocking their cupboards for Christmas in October, instead preferring to wait until later in the year.
It said 32% fewer shoppers than last year had already bought Christmas puddings, suggesting people were not trying to spread the cost of their purchasing - findings that contrast with comments from Sainsbury's last week.
Separate surveys published on Tuesday by payments processor Barclaycard and the British Retail Consortium showed businesses fear a gloomy Christmas ahead, with almost half of households planning to cut festive spending and sales already falling sharply in inflation-adjusted terms.