It has been argued by Birt that without his changes and his readiness to appease the Thatcher government, the BBC's operating charter might not have been renewed in the 1990s. Birt's advocates include the journalists John Lloyd, John Simpson and Polly Toynbee. Birt's use of impenetrable jargon became known as "Birtspeak", a phenomenon mocked in the satirical magazine "Private Eye", complete with a miniature Dalek caricature of Birt. The comparison originated from playwright Dennis Potter, who labeled Birt a "croak-voiced Dalek" in his MacTaggart Lecture delivered in August 1993 at the Edinburgh International Television Festival. The BBC's post-production department made a Christmas tape casting Birt as Davros, the head of the Daleks, which was alluded to many years later on a BBC DVD commentary for "Genesis of the Daleks" by former director David Maloney. Journalist Mark Lawson wrote at the time that Potter's "tendency towards unfocused vitriol and noisy self-examination made his contribution easily swattable by the BBC's damage controllers". Birt himself did not agree with his critics' portrait of the BBC of the time, but did allow that drama was a source of concern. "The originality is not there as it was in the Sixties", he said.