For those of you doing the Constitutional and Administrative Law module for your law degree, you will already know a lot about the apparently unwritten rules that are binding parts of the constitution by implied agreement from everyone effected by them. Well things may be changing when the draft Cabinet Manual is completed.
This seems to me like a chicken-and-egg situation. The cabinet manual is publicised as a manual outlining all the laws, conventions and rules that effect the operation of government. But we already know that constitutional conventions are generally unwritten, and they are unwritten for a good reason. Constitutional conventions are created by necessity...and they last as long as they are needed. They are 'ratified' by conduct, or oral agreement.
One such agreement is the Sailsbury Convention, that agrees that the Lords will not oppose anything that was in the governments manifesto. The commons is elected, the lords is currently unelected. It would be wrong for an unelected house to opposite a policy that a governement was elected on the basis of. This isn't legislation, it isn't royal prerogative, it is a convention. If the House of Lords became an elected house, the Sailsbury Convention would no longer be required...in fact its existence would be undemocratic. The great thing about a constitutional convention is that nothing has to be done for it to fall out of use.
So of the Lords became an elected house, both houses would just stop observing the Sailsbury Convention.
The risk of the Cabinet Manual is that it gains the status of a binding document...a constitutional convention in itself. It gives the civil service and government a way of 'back door' legislating over procedural matters of the legislative branch of our constitution. It could become such a politically powerful convention on its own, that its existence is accepted and never challenged, much like the convention that none of the main parties challenge the speaker's seat during an election. This defeats the object of a convention, as steps would need to be taken to remove it from the manual for it to no longer be binding.
So the Cabinet Manual is risky, and needs to be something that assists the Executive only and does not bind the Legislature in any way. If this is achieved, i can see this manual being a very useful document handed out to ministers at the revolving door of every department.