The origin of the name Wittertainment lies, primarily, in a discussion that spun off the film Blood Diamond - and therefore probably that movie's most lasting impact on popular culture.
On 15 December 2006, listener Tony wrote in to say "you'll get through all the reviews if you don't witter", in response to the fact that Mark was continually leaving reviewing the film he would name as his Movie of the Week until the end of the podcast, and thus was not having any time to talk about it (Shortbus had been a particular victim of this). Simon replied that wittering was "kind of what we do." Then, on 26 January 2007, Mark reviewed Blood Diamond describing it as "issuetainment" (a word he had derived from Danny Baker, who used to refer to his own show as "infotainment at its most infotaining"). This resulted in various listener contributions on neologisms and other portmanteau words, and listener (William) pointed out that "issuetainment" had a precedent in "genutainment" on The Day Today, in which viewer's films of real accidents were used in a segment called It's Your Blood.
Thus, the "-tainment" riff had been established. By the time the next week's show aired, a page had appeared on Wikipedia under the name "Wittertainment" - defining it as:
"A term inspired by the Good Doctor, Mark Kermode's film reviews on Simon Mayo's BBC Radio Five Live show.
Suggested usage: Wittertainment at its most wittertaining.
In a nutshell, Kermode, the barrel-chested former Queen's guardsman is provoked into ranting by the urbane and erudite Mayo, a perfect foil for the discontemparily-coiffed Kermode. The ensuing witter is surprisingly entertaining. Kermode is undoubtedly a man of many words, a small few of which he unfortunately uses very often. These include, and indeed are exclusively limited to: Guillermo Del Toro, Ken Russell's wife, tertiary syphilis, and some movie called The Exocet, I think.
Although the Wikipedia page was deleted shortly afterwards, the word stuck, becoming shorthand for the Film Review Show itself. Its use has also spread to the show's social media presence, particularly the hugely income generating Wittr app and it's lesser clones Twitter and Snaptat.
The new strapline for the show is to be one of the following: "2 'til 4. 5 Live. Wittertainment. Incomprehensible British banter."
"This is Wittertainment on 5 Live. Stretching defiantly optimistic maxims to well beyond their limits for more that 12 years."