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With the upcoming release of .UK in 2013, I don't think this is a good time to be investing in .CO.UK with speculative intentions. If you study and prepare, you will be able to snag a much much better .UK domain for investment purposes very soon.
I would also add that this is probably the greatest TLD release since the introduction of .COM in the very beginning. There's a good chance that .UK could go on to rise and compete with the all mighty one. These events are sure to put a hurting on .CO.UK in the long run. IMHO