It seems odd that Episode 2 of Hut 33 should be about one of the characters potentially leaving, but it proved to spark a good spat between Archie and Charles.
A foreign posting in Iraq becomes available and naturally it is assumed that Charles will be the one to be sent - he is the linguist after all and knows the area. But Archie won't stand for it. Why should Charles get the foreign posting? He's only just arrived for a start. A game of cat and mouse ensues and the foreign posting is not quite what it appears. Eventually, they have to join forces to wriggle out of their commitments. They are only saved by exterior events and a Fascist coup in Baghdad which was temporarily taken over by the Germans.
And so begins the theme of "being sent abroad" in Hut 33. It's been a common threat in Hut 33 (as it was in Allo Allo; the German soldiers were all worried about being to sent to the Russian Front, which meant certain death, or worse.) In Series 2 of Hut 33, the big threat was being sent to Burma, a land of poisonous snakes and terrifying diseases. Who knows what threats Series 3 will hold?
In any given sitcom, there needs to be jeopardy. One needs to ask 'What's at stake?' If there are no consequences to failure the audience will rapidly lose interest because they don't care about the characters. In reality, the consequences of failure at Bletchley were often too awful to think about, but since our regular characters are not really at the coalface of code-breaking, there is less at stake. So failure, for them, needs to be punished in other ways. Being sent abroad was one of them.
Of course, the greatest thing to be avoided is 'losing face' or being seen to be wrong. Pride is one of the great sitcom motivators - and in that it really does resemble real life.