The Jacobite Restoration
I've put this up on another thread but I think it has possibilities. POD is the death of Princess Anne in childbirth in 1700 soon after the death of the Duke of Gloucester. With her death ends the Protestant Stuart branch.
The nearest Protestant line is that of Sophia of Hanover, who would become Queen Sophia I. Many, even among the Whigs, despair of a German princess succeeding followed by her Hanoverian son, George Ludwig.
In 1702, before the young James Francis Edward Stuart, who succeeds his father, James II, as head of the Jacobites in 1701, can be attainted for treason, William of Orange dies following a fall at Hampton Court.
A deputation of Whigs and Tories go to the Jacobite Court at St Germain and offer young James the throne based on a Regency of Protestant nobles and his willingness to recant the Catholic faith. In exchange, England will cease any military action in Europe against Louis XIV and involvement in the War of the Spanish Succession.
After much soul searching, James accepts and returns to London on September 1st 1702 as James III. He publically recants his Catholicism and will marry a Protestant princess. The Regency governs until 1706 when James assumes full powers albeit under the thumb of Parliament.
In Europe, France triumphs, a Bourbon is King of Spain and French domination of the Continent is assured for another century.