I do not believe that it is a regulatory matter particularly. Rather it is a civil issue generally falling to any company that feels it may be being abused/exploited to object.
You generally can not register a trademark that is very similar to someone else's especially if you are in the same business and likely to be confused. You most certainly should take care not to abuse/exploit any trademark you do not own. There are many many websites explaining how trademarks work.
Here is one.
You will have seen many companies in the old days with names that feature locations along the lines of:
A N Other & Co (Hereabouts) Ltd
The internet has somewhat opened up a can of worms and it is very easy to register a domain (and many variations are possible) and the registration authorities need convincing of who has the right to use the domain in the case of dispute.
There is nothing stopping me registering the name TescoFood.co.uk but if I started selling food through this and particularly if the site did not make it clear that it was nothing to do with Tesco and did not obviously have a very different brand image Tesco would certainly object (when and if it noticed and there are companies around who monitor these things for the big boys) and possible would sue me. A civil matter.
The Police would only become involved if there was some criminal activity around what I was doing, primarily some kind of fraud (obtaining money by deception).
Domains names based on ordinary English words are problematic. How about windows.co.uk?
There were a lot of problems a few years ago with companies with the same name but from different countries arguing over who had rights to the .com version of a domain of that name. For a while, the default answer enforced by the registration organisation was the USA company had primacy (by the way, not a lot people realise that there is a country domain for the USA it is just not used much).
If you name a company and/or use a domain, in a way that it can be viewed (on the balance of probabilities) to be trying to exploit the "good will" of another established company then you will almost certainly face problems sooner or later.
If the name uses common words though and is not obviously moving into well occupied territory (in terms of identity) you should be fine.
Stuart