Yes, buy both. There is bound to be the same street name in other parts of the world.
I've had (got) names with both extensions, and the stats show more hits on .com's than .co.uk names; even for U.K based names.
type the name in browser without tld and just press enter you will get the answer and the answer it Dot Com.
though English is the common language for Web and for UK so dot Com is enough.
But if you are registering the name as development and having a good outlook for that name then register Both extension.
If both are available to register than absolutely buy both. It's a minimal investment. If you have ZERO plans of going outside the UK than use the co.uk domain and like others say forward the .com to the other. Which one to use would be a personal preference and also a preference of what is perceived as normal in your country. If all you see is co.uk than you have to use that one but if .com is used and accepted and is widespread I would use the .com just in case you ever wanted to branch out of the UK market. If you ever have plans on selling the website at any point than having the .com also is a huge bonus and only costs you 8 bucks a year.