HuskyPup - 2:25 pm on Sep 28, 2012 (gmt 0)
Buy both and point the .com at the .co.uk.
The game has definitely changed in the last couple of years and .co.uks definitely rank better than .coms, in fact I have had to duplicate my 17 year old .com on to my .co.uk since I lost so much UK traffic whilst still doing well outside of the UK.
The most annoying thing is that I sometimes see US .coms in the UK SERPs that don't have a chance in hell in supplying my widgets because we supply them!
Overall the .co.uk SERPs have been in quite a mess for 18-24 months now and I do not see them getting any better.
To test which works best log-out of personalisation, clear your cache etc and then type in a few keywords etc and see what comes up. In my widget sector it is dominated by .co.uks these days.