Rachel Kettle wants to know what happened to Jed, the red-haired technician who appeared throughout series 1?
Although this hasn't been revealed on-screen, the answer might well be found on the DVD release of series 1. A couple of scenes were filmed for series 1, episode 6 but cut for timing purposes in which Jed was seen gossiping with an attractive female new recruit. On seeing Harry enter the office with a bunch of flowers, Jed speculated that the very-much married Harry was conducting an affair with another woman. Later on in the episode, an angry Harry would have been seen to correct Jed, pointing out that he regularly places flowers on the grave of his friend (who presumably was the one killed by the Irish Republican Patrick McCann). Considering how Harry effectively sacked Tessa without losing too much sleep, it's possible that he also arranged for Jed to be transferred to another department.

Richard Foster has picked up on a small discrepancy between the Radio Times and your friendly neighbourhood [spooks] expert. He writes: 'I saw your claim that there are 10 episodes this season, yet the Radio Times is advertising episode 6 as being the last in series 2. Who is correct?'
I could say keep watching and find out to maintain the surprise, but for those who don't want to know, look away now...

I'm right. Promise!

Bobby MacGregor asks:
'Technically, do MIs 1 to 4 still exist?'
When the original Secret Service Bureau became part of the Directorate of Military Intelligence in 1916, there were already a number of departments assigned an 'MI' number. MI1 handled Codebreaking, MI2 covered intelligence to do with Russia and Scandinavia, while the rest of Eastern Europe came under the remit of MI3. MI4 looked after 'Aerial Reconnaisance', and so on. The other MI departments were either dismantled or else their work was absorbed into that of MI5 and MI6, and later the Government Communications Headquarters - GCHQ.

Richard asks:
'Who is the actor that played Ibhn Khaldun? He looks familiar.'
Ibhn Khaldun was played by Alexander Siddig, perhaps best-known to fans of Star Trek: Deep Space Nine in which he played Dr Julian Bashir. Formerly known as Siddig El Fadil, the Sudanese-born actor changed his name after finding many people couldn't pronounce his name.

David Cleland asks:
'In series 2, episode 3 the Spooks were trying to contact agents in the field in a foreign country when the hacker attacked. Surely this is wrong since MI5 is responsible for domestic counter-intelligence, whereas MI6/SIS is responsible for foreign intelligence gathering? Was this merely a plot device?'
You're right to make the distinction between the remits of MI5 and MI6. However, there are many occasions when British interests abroad are protected by MI5 rather than the Sister Service, MI6. Such instances might include the protection of diplomatic premises and staff, British companies and investments, and British citizens living or travelling abroad. In the episode in question, the arms fair that the two agents were infiltrating presumably had some links to British interests.