I'm struggling to get everything down in the instalments so will provide the rough framework that I was going to use going forward...
1840
Edward Oxford shoots Queen Victoria - she dies meaning the crown transfers to her uncle, Ernest Augustus, Duke of Cumberland and the King of Hanover.
However it will take at least a fortnight for Ernest to be informed and travel to London, and for that period the government wields almost absolute power despite the Duke of Sussex being nominal Regent.
Thomas Peronnet Thompson approaches the Prime Minister about disqualifying from the line of succession. Melbourne refuses even though he knows Ernest will be an awful monarch.
Peel - the Leader of the Opposition - also refuses though he's more open to the idea.
Prince Albert and the Dowager Duchess of Kent make plans to move from Buckingham Palace to Claremont House in anticipation of Ernests arrival - neither like him.
Leopold, King of Belgium, arrives to help comfort his sister and nephew at Claremont House.
Ernest finally arrives in London and claims the crown - having left his blind son, Prince George, as Viceroy in Hanover - he doesn't wish to install the Duke of Cambridge as Viceroy again because his brother is more charismatic and he worries Hanover might remove him from the throne and install the Duke of Cambridge.
Instead he recalls the Governor of Canada, Lord Sydenham, and sends Adolphus and his family to fill that position instead.
He deals with the Duke of Sussex by sending him to France to act as Ambassador to the French Court of Louis Phillipe.
Ernest tries to exert authority in Parliament (over amendments to the 1829 Catholic Relief Act and an increase to the crown allowance) and the Commons pushes back, but in order to get his own way, he creates peers who will vote how he wants them to. Melbourne protests but the protests are futile.
Peel and Melbourne argue in Parliament, with the unbalance in the Lords making a continuation of Melbourne's ministry untenable. Melbourne resigns and the Home Secretary, Constantine Phipps, Viscount Normanby becomes PM.
Phipps is rather more cautious about challenging Ernest than Melbourne was, and subsequently the monarch begins to regain powers.
With the appointment of a new Prime Minister, a General Election is called and politicians split into two factions - either Ernestinian or not-Ernestinian (called The Kings Party and The British Party).
Melbourne has left the country and the leading figure in the not-Ernestinians is Thomas Peronnet Thompson. However, Thompson is assassinated whilst at a rally in Manchester and all clues point towards Ernest being responsible in that matter.
Phipps continues to meander as Ernests puppet and crown immunity is implied, Ernest doesn't even really bother denying that he orchestrated the assassination.
Drummond, Melbournes private secretary until his resignation, becomes the leading anti-Ernestinian figure and decides he will approach Ernests sister Princess Sophia about supporting their cause - as he was instructed that she held information that would help smear Ernest.
This revelation would involve her admission of the parentage of Thomas Garth which had heretofore been only rumoured. This would smear the whole royal family if revealed as it would implicate that they knew about it and covered it up.
Meanwhile, Melbourne, out of guilt for the explosive state of British politics has taken up Thompsons cause and has approached William of Wurttemberg at taking on the British crown in return for supporting the coup against Ernest (he bypasses the Brunswicks because they are either unpopular or unsuitable - Charles abdicated, William is unliked, and immediate royal family) - and in France, the Duke of Sussex is revealed to have found the (nation) are supporting a movement to overthrow Ernest and George in Hanover but chooses to remain silent on the matter.
Note: One idea that I was considering but was unsure on how to implement would have been a 'League of Extraordinary Victorians' - including Ada Lovelace, Charles Dickens, Isambard Kingdom Brunel that would have sided with the Anti-Ernestinians.