(Yesterday, 4:49 pm)Superman wrote Risk mitigation basically, primarily against potential traffic commissioner issues (fines and stuff are weighted by the o licence size, so you could imagine why they keep them split, to some degree, for protection).
Pretty much why most operators split their licences to be fair. Limits any impact on undertakings etc.
Correct me if I'm wrong but Arriva Northumbria and North East have different pay rates and working arrangements (a result of them being independent for a while after deregulation).