It's a good start...
But there's still a lot of room for improvement;
Firstly being there's too much text. It's not just me being lazy- that much writing would be better as a narrative, try doing it as a voice over. (Spelling and grammer is ok- but could use a brush up).
The plot is very good- hence the higher rating, but again there were a few bugs that really got to me. (If you're going to follow the Plot from Mortal Engines- check out the official site - you can fill yourself in on the history of the Traction era).
If you're not- then I apologise for the above- and you may continue as you please.
The animation is quite good- but again you can still improve- try shape tweening the map when you show the change from Before to after.
Also just add more- when you mention London - show us London. Show Manchester fitting it's jaws.
Your graphics look ok- there's some nice vector work at the start- but try to stick to one method- using the mouse+paintbrush on the world map kinda messes it up. (it's ok- you're not the 1st to do that!)
And on a final note- just to tidy it up a little, you need to liven up the title a little. Plain text is ok for narration/speech. C'mon its your main title! Pythonic Pistons! Add some artwork, show a little pride! - It should stand out! Jesus Christ- you're using Flash, not windows movie maker!!!
-Sorry, It just really bugs me. Thats all.
But if you only ever have one piece of advice- KEEP PRACTICING
Thats the best way foward.