Calling all armchair generals! Boudica's Last Stand.

[Renatus]

Not sure about that. A direct invasion of Cogidubnus's territory would risk turning a uprising for a very obvious cause (revenge on the Romans) into an inter-tribal British conflict, with corresponding dangers of political disunity in Boudica's force. Even if Cogidubnus was a collaborator, he was still a British king, and would surely have had his own networks of alliance and influence that might have stretched throughout the rebel tribes and their ruling aristocracies.

I suspect that, once the rebellion started, everything changed. It was an all-or-nothing situation and anyone who was perceived to be pro-Roman is likely to have been treated as anti-rebellion and ripe for attack. There is another possibility, however. The rebels may have believed (perhaps with justification) that, if they were seen to be advancing on Cogidubnus' territory, this would encourage an anti-Roman faction amongst the Atrebates to rise, overthrow the king and bring the tribe into the revolt. If that had happened, Paulinus would have lost probably his main ally amongst the British nobility, the smaller tribes would have seen where their interests lay and joined the revolt, and the province would then truly have been lost. Perhaps it was this possibility, amongst other considerations, that persuaded Paulinus to give battle when he would really rather not have done so.