I said .com because the question its self is flawed, no one could advise properly with out knowing what type of site/business it was, how it was going to marketed and what the purpose is.
Everything in this thread is pure opinion based on your own experiences which most of the time means piss all to everyone else.
"In my opinion...."
If your running a sole online business with very little marketing done else where then yes, Google and PPC may well be your main focus which any old domain or extension would suit.
If your running some crappy click bank affiliate throw away site then same apply's as above.
If however your running a brick and mortar business or have an offline marketing plan as a brand, with your potential audience being non-internet savvy people then .com is still the option imo.
The middle aged bloke in the pub will nearly always think of the "internet" as .com , if you have access to protecting your brand and attaining the .com and the uk TLD's then there shouldnt be a question, you should be registering them all.
If redirects are in place or landing pages setup then it doesnt matter where they go, it will land in the right place.
If i was going to start a brand new site tomorrow targeting UK audience, it would be .uk with the .co.uk redirected , a domain is a domain and its not going to vanish so why do you need it to be tried and tested. Stupid post.
Not sure why people are advising .com when it's not an option. Your best choosing .co.uk at the moment and redirect the .uk to it. The .co.uk extension is tried and tested and the most popular uk extension that everyone knows and uses. The .uk may never take off.