[spoilers] Lucas. Just Lucas.

[Saerwen]

Harry in his position should have had Lucas debriefed as a matter of course and especially after the Russians had him all that time and person if he had some sort of trust could have been rebuilt.

Although Ros told him that Harry moved heaven and Earth (can't remember the exact saying) to get him back Lucas had no tangible proof of this and I think in his state of mind he needed proof that he was wanted and valuable to those he left behind.
I think once Lucas was captured Harry closed the door on him and got on with the job in hand. As time passed and Lucas's captivity lengthened perhaps Harry thought he wouldn't come back at all and when he did go and get him back quite suddenly it seemed it threw up a real awkwardness then had he debriefed Lucas who had asked why did it take so long to get him back, what was Harry going to tell him as it seemed he hadn't done anything at all.