IS it more rational to have one command structure for policing across Scotland, regardless of the context, or does it make more sense to have a single command structure for railway policing across the UK, regardless of geography?

According to the police watchdog, you won't find the answer in the Scottish Government's policy memorandum setting out the case for its goal of integrating the duties of the British Transport Police (BTP) in Scotland into Police Scotland.

Her Majesty's Inspectorate of Constabulary in Scotland (HMICS) says there's a reason for that: nobody has asked the question. The uncompromising verdict of a leaked HMCIS report on the merger is that the decision to merge the functions of BTP into those of the single Scottish Force was "entirely" political.

It is unsurprising that as a matter of principle the SNP might wish to see transport policing administered in Scotland rather than at Westminster. The Smith Commission also recommended that the function of BTP should be devolved.

However this does not absolve ministers of the responsibility of considering what the costs and benefits of such a move might be.

The HMICS report says such an analysis has not been done. As a result there has been no "authoritative" business case setting out the benefits of changing the way the railways are currently policed – or addressing any possible risks.

The draft report says these include the cost implications for Police Scotland or the remaining UK end of BTP. No consideration has been given to how railway policing may be affected or the advantages or disadvantages of a "dual command structure" across the UK.

The watchdog is also set to cast further doubts over the effectiveness of the Scottish Police Authority – saying it currently lacks both the capability and the capacity to manage and deliver a programme of this scale.

Rail operators, who fund the BTP, have not been given the opportunity to agree the change. Some fear being left to foot the bill for a possible overall increase in the cost of transport policing. HMICS agrees that they should have been consulted.

The document may yet be changed before it sees the light of day. But the initial conclusions of HMICS's strategic overview are concerning.

The recent history of both Police Scotland and the Scottish Police Authority has hardly been smooth. It is questionable whether it is wise to hand new responsibilities over an important service to two organisations which have not had their troubles to seek.

Parliament has already seen doubts expressed over the move . Holyrood's Justice Committee considered the plans, but could not reach a consensus. Yet MSPs approved the proposal in June.

HMICS is right to say integration can still be successful, but the Government has a duty to fill in the gaps and make sure they demonstrate this change is born of reason, and not just ideology.