For the moment I have decided to go with the following:
1) Parliament gets enlarged to 750 Members
2) Indian counties/constituencies will be proportionally larger to prevent Indian Domination of Imperial politics
3) Local Parliaments can form their own parties
4) If you want to join the Imperial Parliament jou have to go for one of the established parties or your party must accumulate a certain level of support throughout the Empire. The established Parties will recruit candidates in the various nations. These however must be locals if possible. ( I mean come on, Bermuda and some of the smaller territories....)
5) exception to No. 4 will be India.
6) I have already decided that the PM who replaces Blair will be a member of the INC, the first INC member to move into No 10.
Except for 6) I am open for discussion.
Defence is the next great hurdle.
My proposition is: For now Colonial soldiers, NonComs and Officers serve in the regular British Army. ( This to explain the ridicolously big Armies I will have to build) This is done to provide an experienced cadre. After the war the nations will for their own Army Units and in the case of India also Air units. They will be under the command of the Imperial General Staff, and only in case of emergencies (natural disaster relief etc ) put under local jurisdiction, and that can be done without the consent of Parliament. They also become 'local' forces in case of 'Extreme National Emergencies' i.e. when the UK has been nuked to smithereems or the Command structure is completely destroyed for some other reason. Now for the Navy every subject from every nation who wishes to defend Britannia on the waves will have to join the Royal Navy. No Royal Indian Navy, no Royal Rhodesian Navy and so on. Same goes of course for the Air Force.