They do realize that the Irish have raided the British area since time immemorial?
We'll never know for certain, but it sure looks like Agricola had it all planned out, and may have intended to finish up the conquest, then move the capital of the province to Chester. Until the arrival of the Great Heathen Army, the greatest of the Anglo-Saxon-Jute kingdoms (the "heptarchy") was Mercia, which seems to echo some Roman and Post-Roman reality on the ground.