It’s either a fad or a revolution, but whatever the future holds for veganism it’s set for another flexitarian-fuelled boom next month.

More than 100,000 people have already pledged to stick to a plant-based diet for Veganuary, double the number who took the plunge at the same time last year. The organisation behind the campaign is expanding into Germany, the US and Chile and is airing its first TV commercial after Christmas. “On Sunday, we finished with about 102,000 sign-ups and that is massively more than at the same point last year, 15 December, when we had 44,000 sign-ups – that’s a 127% increase,” Veganuary’s Toni Vernelli said. It hopes to reach 350,000 by 1 January, up from 250,000 at the start of this year. The campaign is having an impact on restaurants and supermarkets, she said: “The number of companies getting in touch with us who are launching products is truly mind blowing. It does just seem to be everywhere.”

Marks & Spencer will have more than 100 vegan products including those in its Plant Kitchen range, with a No-Chicken Kiev, a tofu-based ToFish and Chips, as well as lunch pots and snacks. Aldi has a vegan seasonal range with 10 new items, from sandwiches and ready meals to ice-cream. Iceland will expand its vegan range in January, as will Waitrose, which says its vegan Christmas sales have risen by 40% – all the supermarkets made big additions to their Christmas ranges this year. Greggs, which stole the show last year with its vegan sausage roll, is expected to launch a follow-up and Burger King’s “rebel whopper” may reach the UK. Those products are aimed at flexitarians – people reducing meat in their diets – because though veganism seems to be growing, only about 600,000 people are fully committed to not eating animal products. About half the population are either not eating meat or actively reducing it, according to market researchers Mintel. It was described last week as a “plant-based revolution” by another analyst, Innova Market Insights.

The competition – dairy and livestock farmers – are clearly concerned, although it’s hard to tell exactly how much impact veganuary had last year. Initial reports from Kantar Worldpanel, which tracks consumer spending, showed that sales of meat remained fairly steady at the start of the year.

But since then the firm has charted a significant decline in sales of beef, lamb and pork, although fish and chicken have grown, and a later Kantar study showed that 1.31m people gave up animal products in January 2019.

Although many of the new products mimic meat, fish and cheese, from BBQ ribs and bleeding burgers to Camembert and smoked salmon, some vegan entrepreneurs believe they can persuade people to eat plant-based food that hasn’t been manipulated.

Alex Petrides set up Allplants with his brother Jonathan in 2017 to offer vegan-only food subscription boxes – frozen meals delivered to your door. “We don’t use synthetic ingredients,” Petrides said, “but we do use the language people are familiar with and can connect to. We believe it’s possible to create all the expressions that people have come to expect from food and all the emotional and nutritional qualities purely using plants.”

• This article was amended on 23 December 2019 to more accurately set out the range of vegan products available from Marks & Spencer.