Clearly, if I can't see these ads and I'm in the centre of London, it stands to reason that a great many other potential customers can't see them either. However, if I go UK-wide in terms of the ads, I run the risk of attracting loads of speculative clicks (even though the ads scream 'London') but maybe I'll get more customers.
Any thoughts or advice would be gratefully received.
I'd read through it (I'm a huge fan of running a geotargeted campaign with general keywords, and then a national campaign with geotargeted keywords), and then see if you have more questions about geo targeting.