Er, speaking as an ex-ITV person, hell yes we were responsible for any ad we showed.
All TV ads have to go through clearance and compliance processes to ensure they're fair, truthful and balanced - in fact, to a standard that puts them well ahead of a lot of TV content.
And any time we didn't, the ASA shows up and all hell breaks loose...
"When the ASA feels a complaint is justified, it can take action with the broadcaster concerned. The ASA can require the broadcaster [note: not the advertiser, the broadcaster] to withdraw the advertisement immediately, amend it or suspend it while investigations are carried out."
...and if that wasn't enough...
"For serious or repeated breaches of the Code, Ofcom may impose sanctions, ranging from a formal warning to a request for broadcast correction or a statement of findings, a fine or the shortening, suspending or taking away of a licence to broadcast."
Even in the cosseted world of ad salesmen where breaches of personal conduct were common and the odd bit of dodginess tolerated, if your screwup causes the ASA to do so much as send a pointed email, it's a career-ending move. As in "never eat lunch in this town again".