A paper from the Federal Trust - A Federal Future for the UK: The options.
The flexibility about the precise size and number of English regions works in the opposite direction as well: it would be possible to have more than nine regions. Partly depending on how a federation is centrally organised, having more units of smaller size is arguably not a problem in the way that an overlarge component might be: the US manages with as many as 50 states; while Germany has 16. Nor need great variance in the size of the components of a federal UK be a problem. The US has states that range from under 1 million (Alaska) to over 35 million (California). Consequently there is no reason a territory such as Cornwall, with a population of around half a million, could not be a single component in a federal UK alongside other larger units. By this means strong regional identities such as that of Cornwall could be harnessed in order to facilitate a more cohesive federal UK.
The main text of Cornish interest from the paper is copied above but more can be found in a document well worth a read. Are our politicians and decision makers taking note?