Mark J says:

if you have a registered company which uses the same name as your proposed website then you have prior claim on web addresses in the same country of origin as the TLD ie “.UK”. assuming that the busines is already trading and the website(s) are up and running then you have prior claim.
someone can take out a trademark application (as indeed so can you – see tha patent office website; its not that expensive). if they make an applcition for ther trademark and its successfull and its in the same area as you then they have prior rights to the name, but not the website address. if there is an applciaiton in the pipeline, you can object to the applciation, however you have to show grounds for your objection (ie you are already using the name).
im not entirely certain what the precedence is one company has a trademark in your area of business (geographicaly and business type) and another enitity which has the same comapny name and website addresses. I suspect it could go on whoose been actively trading / using the name for longest.
If someone else owned the trademark then they cannot stop you using the company name – if youve registered the name then its yours. no one can take that away from you, unless you want to sell it. UK company law is different to trademark law or accepted custom and practise in the web world.
bear in mind it only is a problem if the company AND trademark holder are in the same business area. someone could own the trademark for your name in another country – thats irrelevant in UK law, although there could be problems with the harmonised EU wide patent law). A potential issue is that a .com address is deemed to be a US TLD and therefore would be covered by US law – sugegst you lok at the TLD domain registrar for their rules.
say your comapny was ultrawidget.com sells computers, and a company making fasteners had the trade mark “ultrawidget”, its unlikely that they could stop you using the name ultrawidget for your business or web address (becuase they are not in the same business sector), even if they did you could change the name to “ultra-widget”, or “UltraWidget”.
if you have a already have a problem it may be worthwhile to sound out a law firm sepcialising in patent law and see if you can get a defintiive opinion if your business is serious about the name.it will probably cost you around £2..500 to register the trademark in the UK, US & Europe [Its a one off fee]. if you dont plan on trading in the US, and dont want to use a .com address then I wouldn’t bother registering in the US.
do a search on the UK & US patent office websites and see if your comnpany / web name is already trademarked if not you can register the trade marks yourself, providing you know the correct busienss sector (thats why I’d suggest using a patent lawyer to make sure the application is made in the right manner- its relatively cheap and shouldnt be a a big bill if the business is serious about its name).

Jester says:

If you have registered the domain name, nobody else will be able to use that domain. However, lets say you have registered Mycompany.com, there is no reason why somebody cannot come along and register My-Company.com or Mycompany.co.uk or Mycompany.net etc. etc.
So my advice would be to purchase the .com, .net, .co.uk etc. etc.
If you would like more info on Domain name secrets, send me a mail, I would be glad to help