For a generation of households that grew up with his Turkey Dinosaurs, Twizzlers and Golden Drummers, he was the tweed-suited tycoon with the "bootiful" catchphrase who brought convenience and a touch of playfulness to midweek tea times.

To the growing healthy eating lobby of the past decade, however, Bernard Matthews's moulded poultry shapes represented everything that was wrong with modern industrial farming and food production – all wrapped up in golden breadcrumbs.

And in recent years, critics of the Norfolk turkey baron could barely suppress a mounting sense of schadenfreude as he suffered a series of setbacks, enduring the scorn of celebrity chef Jamie Oliver, writing down multi-million pound losses, fighting bird 'flu, mass culls, and a high-profile prosecution of two contract workers for animal cruelty.

But the young entrepreneur who turned 20 eggs and a second-hand incubator into a successful agri-businesses 60 years ago is about to see it embark on the latest stage of a turnaround by re-inventing the brand as Britain's largest farmer of free range turkeys.

The acquisition of nearby rival Lincs Turkeys this week means that Mr Matthews will boost its output by a million birds a year to eight million – more than doubling the number of outdoor turkeys it has to 600,000.

The company hopes this will meet demands for poultry which can wander outside, as well as countering the public's distrust of "standard" indoor birds, which are farmed in large sheds containing thousands of birds. But even after the latest, £23m acquisition, only 7.5 per cent of Mr Matthews's turkeys will be free range, with a further one per cent conforming to the basic standards of the RSPCA's intensive farming mark, Freedom Food.

Campaign group Compassion in World Farming wants poultry companies to be forced to inform customers about the conditions their birds are kept in, on food labels. Steve McIvor, its director of food business, said existing basic guarantees did "nothing to prevent the serious welfare issues of high stocking densities, fast-growing breeds and many mutilations, particularly beak 'trimming'."

The Soil Association's technical manager, Anna Bassett, cautiously welcomed the takeover. But she added: "What they are doing is seeing what the market wants and trying to meet it rather than changing from a philosophical belief that all these turkeys will be better off outside."

Under the leadership of the marketing veteran, Jeff Halliwell, the East Anglian poultry producer is in the middle of a four-year transformation, a key plank of which has been promoting the "super food" qualities of the low-fat, high-protein meat.

It has ended controversial imports of birds and brought back the "bootiful" slogan first aired in 1980. Mr Matthews, who cradled turkeys outside the firm's Great Witchingham Hall headquarters in the television adverts, stepped down as chairman in January, aged 80. Financially, the company's outlook is improving and figures next month are expected to show an increase in turnover and profits.

"All our birds are raised to the Farm Animal Welfare Council's guidelines and we are open to inspections at any time from the RSPCA and the major retailers," said Mr Halliwell.