Like you said, Mr. Clean Magic Erasers are the way to go. They're actually nothing like "erasers". They appear as very light white sponges with a very fine grain texture. You have to wet them (either whole thing or a corner, I cut mine into smaller pieces) and then squeeze them until they are just moist. The harder you press, the "more" dirt it takes off. For example, don't press very hard if you wipe a key on your keyboard with it or you'll take the letter right off.
They don't sell them in the UK? Stores around here have their own brands of them, like Walmart's Great Value brand of "Super Clean Eraser" and knock off products.
There's nothing really comparable. I used to use a cap eraser that you would put on the end of a pencil, but then I would have to use another cleaner in order to get the eraser marks off. It took me 45 minutes to clean my 2 palm rests this way. With the magic eraser, pressing with NO PRESSURE, I just wipe each palm rest, and wipe with a paper towel real quick before the dirt dries back on it. It's awesome!
You could always have someone buy you some and then ship them to you. If you cut the up into little pieces (they're like half a small brick and they come 2 in a package) they last a while. I used the same 1" x 1" piece almost 10 times already, because you don't have to press at all for the palm rests.
Here's how good they work. My clamshell had permanent sharpie marker on the outside lid (was a "54" because it probably belonged to a school or organization). I had to press quite hard, but there's no trace of the 54 anymore. That's crazy! Pressing hard like that makes the magic eraser disintegrate though, but that's ok.
All in all, <3 Mr. Clean.
