[spoilers] Lucas. Just Lucas.

[BoHenley]

I think that linking up with Maya again has unhinged him. He's not a traitor, but he is (currently) betraying his team to cover his butt, and digging a deeper and deeper hole for himself. Until we know what happened in Africa (speculation: civilian deaths) it's a hard call on this. His character in 7 and 8 was fastidiously loyal, if a little unorthodox. If there's no twist at the end of this, then it's a character assassination and a betrayal of Spooks fans.