#1: Having a .co.uk websites helps in ranking in UK
#2: Having a .co.uk website helps in better sales in UK as people see personalized.
#3: .com will be for all countries except UK
#4: Adding content on both .com and .co.uk will be difficult, there will be common section
#5: Google allows tags rel=alternative langhref for languages but not for regions in the best way
Now how do one have a website for .co.uk and .com and get the best for ranking.