Dinner/going out attire in London/Edinburgh

[woowoo]

Can anyone give me some guidance on what to wear/pack for evenings out in London & Edinburgh?  I'm trying to A) travel lightly since we're doing a bit of city hopping in Scotland and B) be comfortable as we love to walk/explore.  We'll do a couple of nice dinners and will likely go out to bars/lounges in London (staying in Soho, which I believe is a bit trendier).   Do I need to plan on being pretty dressy?  Can I wear dressy flats?  It's in late May so I'm also anticipating possible chilly weather.  I hear Edinburgh is a bit more casual - can I plan on being in jeans each night there?   

If you're bored and want to support your suggestions with photos that would be fun.     Thank you!