Yes, the British do have some strong units like the head hurlers, druids & chariots but its a very tactful & risky playn style you have to adopt with them when going into battle due to how weak & difficult the chariots really are to use & as for the head hurlers they are very exposed unit which they can be easily picked out by enemy archers if in ranged of fire.. The only strong aspect I've noticed about the British is that most of there units have an effect to reduce enemy moral & increase theirs making them seem very well discipline for a barbarian faction, probably, as equal to the Romans in game.
Yes that will be the conventional way of playn as the Britons by startn a war with Gaul from the start & fighting your way thru France till you reach the Mediterranean Sea by taking Massilia or continuing to march towards Rome, but what fun is that? Its just an easier road to take as with them & won't provide a significant challenge to test your skills as a player...
The road I took with the British campaign I started 2days ago was I decided to ally with the Gaula since both are very identical in culture & people & decide to go at war with the Germans as being more of the challenging neighbor of the two.. My initial plan was to move & conquer the Germans westernmost province Trier & then marching on to Mogontiacum & holding the Germans from there as my main force kept marching south into Noricum & eventually reaching Illyria & developing that area well until I can build boats & start a raid invasion against all non barbarian civilization but it didn't not go according to plan due to betrayal, Dacia rapid expansion westward to Noricum blocking pasture into Illyria & elongated wars against the Germans. This is truly being the challenge I was craving for