Hi all,
I am exploring an alternate history for a children's novel I am attempting to write. In this world Victoria and Albert were assassinated a few months after Princess Victoria was born. The Princess is then sent to live with her family in Belgium - King Leopold being Queen Victoria's uncle - for her own safety.
My question is.... what event would or could prevent the Princess Victoria returning to England to take up her position on the throne when she was deemed old enough? I need a reason that would prevent her from ever actually officially becoming Queen.
What would the consequences be of her marrying the Crown-Prince of Belgium and therefore becoming Queen of Belgium?
So to add some detail to your first point - there would have been a Regency Council, although the Regency Act of 1840 complicates matters as it sort of assumed that Albert would survive Victoria if it came into effect. In reality you'd see a mixture of the Royal Family (the Duke of Cambridge is still kicking around and up until 1849 you have Queen Adelaide too who few would have objections to) and politicos - probably prominent figures like Melbourne, the Duke of Wellington, etc. You've also got Victoria's mother (this Victoria's Grandmother) too, although in 1840 she was still somewhat out of favour at Court.
VII would not be sent to Belgium, although Leopold would agitate for it, but would be kept in Britain. I think suggesting the Tower of London is a bit extreme and impracticable - by this point it was little more than a dusty storehouse really. Much more likely would be the relative security of Windsor Castle. Somewhat of a gilded cage, but still more realistic than the Tower.
She wouldn't be allowed to marry the Crown-Prince of Denmark because of the laws governing Royal marriage to Catholics at the time. It would be almost impossible to change those laws - and the future Edward VII's son gave it a good try.
In this alternative world - Queen Victoria and Prince Albert are assassinated in the summer of 1842. A major fire at the Palace of Westminster decimates Parliament and as a result the Royal Society with his mix of politicians and scientists form a technocratic Government - this leads to Great Britain being more scientifically and technologically advanced - heralding a Steampunk style era - Babbage's Analytical Engine is produced for example. I know this is quite a wild leap but it is a work of fiction after all
This is a very wild leap and also makes quite large assumptions about what the Royal Society actually
was in the period. Until the Government bailed it out in 1850, for example, the RS was struggling to even pay its bills, let alone take on the mantle of Government. The hurdles to forming a "technocratic" government (and remember that's a very modern usage of the term that wouldn't have had much purchase at the time) would be huge. You would need, as other posters have suggested, a very different path for Britain in the period.
Thanks - the idea was that the British Empire is effectively ruled by scientists, but there are small groups who oppose their rule - (such as the New-Luddites) and the more peaceful Pro-Victorians - who want their Queen back.
Poor Luddites. So misunderstood by history.

I'm not sure what you have planned for them, but please be aware that they weren't simple "Down with Technology" rednecks but workers caught up in a very real crisis where machines were destroying decades upon decades of craft skills they had hoped would continue to provide for their children and grandchildren down the line.
I will try and think of a semi-plausible timeline and post later if I can... as it is an interesting challenge.