The Great British Bake Off on Channel 4 has attracted Amazon to be one of the main sponsors by signing up as headline sponsor of the second series, in the US tech giant’s biggest UK TV deal to date.

Amazon is thought to have paid about £5m to secure the deal, making Bake Off one of the most valuable entertainment sponsorships in the UK, alongside Britain’s Got Talent and The X Factor, after the show’s move from the BBC defied critics by proving to be Channel 4’s biggest hit in decades.

Amazon intends to use the show to push its Echo speakers and the capabilities of the Alexa virtual assistant. Bake Off attracted the largest audience of 16- to 34-year-old viewers of any TV show last year.

The final attracted Channel 4’s second-biggest audience ever, having been watched by 11 million people including those who watched it live, via recordings or repeats. As a result, the broadcaster has been able to raise the price for the second series.

The new deal with Amazon is a coup for Channel 4, which previously had to settle for splitting the headline sponsorship between two brands not known as major TV advertisers – the German baking ingredients maker Dr Oetker and the kitchen cupboard staple Lyle’s golden syrup – when an expected bidding war failed to materialise. They each paid a bargain £2m.

Channel 4 paid £75m to poach the biggest show on British TV from the BBC. Advertisers initially balked at signing a big sponsorship deal, not knowing if audiences would follow the new-look show to commercial TV. Only one judge, Paul Hollywood, made the move from the BBC.

Rival ITV sniped that Channel 4 had paid for “baking powder and a tent”, while critics were sceptical of the new lineup, which includes new hosts Sandi Toksvig and Noel Fielding and judge Prue Leith.

“It’s a great testimony to the success of Bake Off’s debut on Channel 4 last year that Amazon will sponsor the Bake Off programme brands this year,” said Jonathan Lewis, the head of digital and partnership innovation at Channel 4.

Amazon’s deal includes sponsorship of the spinoffs Bake Off: An Extra Slice, hosted by Jo Brand, and Bake Off: The Professionals, as well as celebrity and festive specials.

Despite fears of advertisers looking to move away from TV advertising to digital, major online players such as Amazon, Apple and Google have become serious spenders on traditional media.

Amazon is investing the most in traditional media such as TV, cinema, radio, press and outdoor advertisingof all the big online businesses. Its TV ad spend accounts for just under half its total £83m ad spend last year, according to Nielsen figures.

The Bake Off sponsorship is Amazon’s most significant strategic marketing move since the company sponsored ITV’s Downton Abbey in 2014 in a two-year deal worth about £8m.

“The industry spends a lot of time talking about the tech giants and the challenges TV faces from a competition perspective for advertising,” said one senior executive at a major media buying agency. “It is interesting that such a big behemoth like Amazon have targeted one of the biggest shows on TV to promote one of its leading products.”

Amazon is committing tens of millions of pounds to marketing as it seeks to win the battle to keep Echo and Alexa, which can perform functions such as making shopping lists and playing music, ahead of rivals such as Google Home in the hotly contested voice command product market.

Amazon recently spent almost $4m (£2.8m) on a star-studded Super Bowl ad to promote the products – featuring Gordon Ramsay, Rebel Wilson and Sir Anthony Hopkins as well as its founder Jeff Bezos.

The Bake Off deal comes as rival Netflix announced it is to make the first seven series of the show available on its service from Saturday. Netflix was interested in buying the show when it moved from the BBC, but makers Love Productions desired to keep it with a free-to-air broadcaster.