So how about a successful Jacobite restoration in 1715, which is never really accepted by the people. The new King has a decade of feuding with parliament, during which time the armed forces are neglected, and then low level resistance breaks out, eventually erupting into full blown civil war in the 1730s. This is long and messy, and not only destroys a lot of the capital needed for the coming industrial revolution, it also smashes British overseas trade, further weakening future conditions.
New England, paranoid of Catholic takeover, then declares independence, and successfully becomes its own country. Skirmishes break out in the rest of the colonies between different groups of supporters. Back home, the Jacobite King eventually falls and some prominent Whig magnate (Newcastle?) seizes the reigns of power. He raises taxes to a very high level to fund regaining control of Scotland, Ireland and the American colonies, and ends up drawn into long bloody wars. Resentment of this sees a Tory backed military coup, which restarts the civil war. Eventually, England emerges as an military state, hostile to the Whig merchants, and has to cede its American colonies and recognise independent regimes in Scotland and Ireland.
Meanwhile France takes advantage of British problems to knock them out of India and also builds trade with New England. The extra funds from this and weakness from Britain means it is able to grab the Austrian Netherlands during wars with the Habsburgs. A combination of extra trade and more raw materials in the new Eastern provinces cause greater economic growth and a bit more of a middle class than our timeline. However, the absolute monarchy is holding back these merchants, and when a financial crisis hits in the later part of the century, they push heavily for the end of feudalism during the calling of the Estates-Generale. Eventually, they manage to grab control of the revolution and place Philippe Egalite on the throne, who avoids aggressive wars but defends France's borders and brings in various capitalist reforms. Soon the industrial revolution spreads to Prussia, who is an emerging power at Austria's expense.
Come 1820, France and Prussia are the two leading powers in Europe. Britain is a screwed backwater.