I am sure there are a few UK YC startups. Below is what I can recall off the top of my head.

The blogs in particular may hold useful info for you regarding getting visas and working in the U.S. plus the journey in startup as a whole - I particularly like http://www.kulveer.co.uk and http://blog.harjtaggar.com who are the http://www.auctomatic.com guys as they give a good level of detail throughout their journey.

However, http://www.techcrunch.com/2008/05/02/coming-to-america-getti... (or http://is.gd/1Vrf in short) by Peter from ClickPass could be what you were referring to and probably holds most of the answers you want in the most succinct form.

Anyway, I'm sure if you contact them they may be answer specific visa questions from their experience. Hope this helps.

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  http://www.auctomatic.com
  http://auctomatic.com/about
  http://news.ycombinator.com/user?id=kul
  http://www.kulveer.co.uk
  http://twitter.com/kul
  http://news.ycombinator.com/user?id=harj
  http://blog.harjtaggar.com
  http://twitter.com/harjeet
  http://news.ycombinator.com/user?id=pc
  http://www.collison.ie/
  http://twitter.com/patrickc
  [John Collison]
  http://twitter.com/collision
  
  http://snaptalent.com
  http://news.ycombinator.com/user?id=sharpshoot
  http://sharpshoot.blogspot.com/
  http://twitter.com/sharpshoot
  
  http://www.songkick.com/
  http://www.songkick.com/team
  http://news.ycombinator.com/user?id=ian
  http://twitter.com/soundboy
  http://news.ycombinator.com/user?id=petesmithy
  http://twitter.com/petesmithy
  
  http://www.clickpass.com/
  http://news.ycombinator.com/user?id=immad
  http://www.immadsnewworld.com/
  http://twitter.com/immad
  http://news.ycombinator.com/user?id=petenixey
  http://www.webkitchen.co.uk/
  http://twitter.com/petenixey
  
  http://webmynd.com/
  http://webmynd.wordpress.com
  http://news.ycombinator.com/user?id=amirnathoo
  http://twitter.com/amirnathoo
  
  http://www.scoopler.com
  http://news.ycombinator.com/user?id=ajmalasver 
  http://blog.projectbluespark.com/
  http://twitter.com/_aj
  http://news.ycombinator.com/user?id=dilanj
  http://meonearth.blogspot.com/
  http://twitter.com/_dilan