House of Lords
Just over 100 directly Elected Lords chosen by the people from the traditional counties would be a system that could not be abused by boundary changes.
Would lessen the strain on the UK parliament allowing them to focus on the Whole of the UK and it's territories while allowing the English parliament to deal with matter in England. Would also allow other smaller political parties in England to be actually acknowledged and allow their policies to be scrutinised at a higher level.
Mandatory Coalition has not delivered effective Government in Northern Ireland as a Government which is constantly trying to score political points against itself is not focused on it's job. Lacks official Opposition to scrutinise it's policies.
Devolved nations get a say in UK matters but the Overseas territories don't, although this could previously be justified due to the distance, modern technology would allow representatives to keep in touch with their constituencies whilst in the UK. In cases of Gibraltar and the Falkland isles this would strengthen the argument against Spain and Argentina as the BOTs would then be directly participating in UK government.
A constitution setting out the rights of the people and the role of bodies such as the Monarchy, Parliaments and Courts would help clearly define purpose and allow the Monarchy's role to be updated in line with the 21st century. EG. The Monarchy's role is (in part) to Ensure that the Constitution is Upheld and the basic human rights of British citizens are not being infringed, this is achieved through The Supreme Court whose Justices are appointed by the Monarch.
The Supreme Court can have Acts of Parliament brought before it if they are deemed to be encroaching on the rights of the People. The Supreme Court may also have Bills from Devolved Bodies brought before it should they appear to be overstepping the mandate of the devolved body
The UK parliament of Westminster is responsible for governing over Great Britain, Northern Ireland and Overseas Territories in all matters which have not be devolved to any other body and for the Protection of these Lands through the Armed Forces.
The Devolved Bodies of the Constituent parts of the UK and Overseas territories are responsible for governing within the areas to which power has been devolved.
Something like that…