ITV bosses have threatened legal action over a Channel 4 programme in which Coronation Street actresses were caught up in a sting operation aimed at exposing stars plugging freebies.

The forthcoming investigation for the Dispatches series is reported to have set up a booth at a ‘gifting event’, attended by Coronation Street names, with a view to getting the stars to promote products on Twitter. Other genuine firms had stands at the event in a Manchester hotel.

ITV has written to producers of the C4 show claiming that it makes ‘highly defamatory’ allegations and warning that legal action could follow if the station broadcasts it.

Programme-makers are reported to have set up a fake brand called Puttana Aziendale – which translates from Italian as ‘corporate whore’ – which produced an anti-ageing skin toner and an energising bracelet.

Among those pictured carrying bags for the fake brand at the event were actresses Catherine Tyldesley and Brooke Vincent. However Brooke merely appeared to say thank you for the bracelet in a later message on Twitter.

The aim of the programme was to examine whether stars used Twitter to plug products in contravention of Advertising Standards Authority rules which say that it should be made clear that plugs for free products are adverts.

An ITV spokeswoman said: “The programme has made allegations that are false and highly defamatory and we have written to the producer threatening legal action if they decide to broadcast.”

It is understood no transmission date has been set for any broadcast of the Dispatches episode.

A Channel 4 spokesman said: “We don’t comment on upcoming Dispatches programmes.”