I would assume that Canon has decided not to repair grey imports, even when charging the customers. They wouldn't make any money repairing them and would much rather you purchases an official UK body.
You buy a grey important then you cannot expect to have it officially repaired in the UK, there are also dubious legal grounds, especially by those companies that circumvent UK VAT.
I'll reword that for you...
How shall I put it?
This isn't new, and it isn't limited to cameras, this is all over the consumer market. It is how companies control a product to a particular region.
Take DVD and Bluray for example. There is a reason they have region codes in the first place. So they can control release dates to a particular part of the world and they know it won't work in another part of the world.
Now, here is the sticking point that just popped into my head.
Is this limited to UK or Europe?
Can a camera bought in say....Switzerland be repaired here?
Because if they say no then they have a problem. Article 34 of the ECT (Treaty of Rome I think...) specify the free movement of goods (and workers). It is how the Polish can come here to work and how we can go buy a house in Spain. So they can't refuse repair a product that they manufactured that is bought within the EU.
What does that bring us? Well, I know DR is not in Europe but if they limit their warrant to UK only then who's to say they honour those that bought in Europe?
So it seems the only way out is say that the serial is fake, since clearly the camera isn't fake and to be honest, there is no reason to put a fake serial on a real camera, unless you steal a lorry load of goods out of Canon's factory and tried to get rid of it on the black market.
So it seems to me, bit of a long shot, that Canon is using this as a tactic to control their product to a specific region. They want to control the sales of their product, the import and export.
I guess they don't take too kindly of you buying it online from the far east and save a lot of money in the process thus removing money away from their Canon UK operation (not Canon Asia). They may not take the same stance if your story is that you got it whilst on Holiday.
I may be talking rubbish but its just a thought.