ITV is "bargain basement" and "has become unwatchable," according to one of the channel's most senior production executives, Andy Harries.
Harries recently commissioned a new series of Cracker
"There is too much clutter, and it is putting people off," he said in an interview with the Guardian.
The channel, which has suffered low viewing figures over the summer, had "lost its focus" under outgoing chief executive Charles Allen, he added.
Harries, 52, is a contender to replace Allen when he leaves in October.
He is currently controller of drama, comedy and films for the company's in-house production arm, ITV Productions.
I don't think our drama is big enough, or must-watch enough
Head of drama, ITV Productions
The ITV company has seen a 4% drop in its overall net revenue from advertising in the past year - although profits grew by 12% to £173m.
There have also been relatively poor ratings for the reality show Love Island, which has consistently failed to beat Channel 4's Big Brother.
Analysts have put the group's difficulties down to rising competition from digital TV stations, which has resulted in fragmented audiences.
However, Mr Harries claims "the channel is not as good as it should be".
Love Island has suffered poor ratings this summer
"I don't think our drama is big enough, or must-watch enough. We've had too many series and we have lacked conviction.
"There's been a deep complacency, combined with arrogance. ITV has been caught napping big time."
"ITV is so unfashionable. It doesn't have to be like Channel 4, but it should be modern."
However, Harries points out that new series of award-winning programmes like Cracker and Prime Suspect are due to return to the channel.
He says he hopes they will be "part of a very strong re-emergence of ITV drama".
ITV is to confirm the highlights of its autumn schedule at the Edinburgh Television Festival, which takes place from 25 to 27 August.
According to a spokesperson, Victoria Wood, Ray Winstone and Julie Walters will all appear in forthcoming dramas.
Other stars in the channel's line-up include Billie Piper and Rupert Grint - who plays Ron Weasley in the Harry Potter films.