The background

When writers Richard Curtis and Ben Elton decided to set the final series of Blackadder in the trenches of World War One, the concept was met with some scepticism by some BBC execs. Surely that notoriously brutal and bloody conflict didn't lend itself to a sitcom?

Yet, as far as Curtis was concerned, it was perfect. "The war, or at least the lead up to it, actually was funny," he explains. "We have all these people brought together, meeting other social classes for the first time, everyone completely and obliviously gung-ho about it all. The first hundred pages of any book on the war are hilarious, and then of course everybody dies." It was the combination of humour and horror that would inform the series ? particularly the great final episode.

Making it happen

Goes Forth saw the return of Tim McInnerny as a regular member of the cast. Having played Lord Percy in the first two series, McInnerny was cast in the fourth as Blackadder's enemy Captain Cartwright. But, just before filming commenced, Stephen Fry recalled a boy he'd gone to school whose surname ? Darling ? had been a huge source of embarrassment. And so Captain Cartwright became Captain Darling, one of the most memorable characters in the series. In fact, he proved too memorable for McInnerny himself, who got so used to performing the character's nervous tick that it stayed with him for two months after filming!

And speaking of nerves, Rowan Atkinson's nervous stammer ? a lifelong trait he is generally able to control ? actually brought filming to a stop in one episode. It's the one with Lord Flashheart, when the latter's tendency to shout "Woof!" inspires Blackadder to say "It's like Crufts in here". The original line had Battersea Dogs' Home instead, but in take after take Atkinson was unable to articulate the "Bah" sound of "Battersea". (The letter "b" followed by a vowel has always been a bit of a niggle for him ? which is why Blackadder's voice seems to strain whenever he mentions the name of the female character Bob.)

Look, it's him off that thing!

Goes Forth, like the three series before it, has its share of celebrity cameos. Perhaps the most significant is Miranda Richardson's turn as an army nurse ? a composed and sly performance that's rather different to the shrieking Queen she played in Blackadder II.

The series also features comedy veteran Geoffrey Palmer as the aloof and clueless Field Marshall Haig, as well as Ade Edmondson as the Red Baron ? arch-nemesis of Lord Flashheart (who is of course played by Edmondson's long-term collaborator Rik Mayall). And if you really want to show off to your mates, you can point out that one of the soldiers in Blackadder's firing squad is the acclaimed alternative comedian Jeremy Hardy.

The cunningest episode?

There's very little room for debate on this one: the greatest episode of Goes Forth must surely be the last one ? Goodbyeee.

For one thing, it allows us to hear Baldrick's war poetry, which clearly surpasses the petty scribblings of Siegfried Sassoon and Wilfred Owen. (Sample lines: ?Hear the words I sing / War?s a horrid thing / But still I sing, sing, sing / Ding a ling a ling?)

But, perhaps better even than that, it is a seamless blend of gallows humour and rich poignancy, with the whole motley crew finally facing the "big push" ? also known as certain death. Old rivalries are put aside and Blackadder even shows respect for Captain Darling as they prepare to charge into No Man's Land. In the original script they were all instantly shot dead as they went "over the top", but fortunately this was altered to have them charge in slow motion towards oblivion, before the screen is filled with a field of poppies. A fitting end to an iconic series.