Unless it’s an existing company name/trademark then anyone can register a domain name so long as it follows the naming rules. Actually even if it is an existing company name you could do it but it’s unlikely that your stake would be recognised – this happened fairly regularly when the WWW was starting up.
So you’d be unlikely to be able to register whsmith.co.uk but you could register willsmithfireplaces.co.uk or whatever so long as it was available.
Run whois against the domain name to see if it is genuinely registered.
whois whsmith.co.uk
Domain name:
whsmith.co.uk
Registrant:
WH Smith High Street Limited
Trading as:
WH Smith High Street Limited
Registrant type:
UK Limited Company, (Company number: 6560339)
Registrant’s address:
Greenbridge Road
Swindon
Wiltshire
SN3 3RX
United Kingdom
Data validation:
Nominet was able to match the registrant’s name and address against a 3rd party data source on 10-Dec-2012
Registered through:
NetNames Limited
URL: http://www.netnames.co.uk
Registrar:
Ascio Technologies Inc. Denmark ? filial af Ascio Technologies Inc. USA t/a Ascio Technologies inc [Tag = ASCIO]
URL: http://www.ascio.com
Relevant dates:
Registered on: before Aug-1996
Expiry date: 23-Sep-2017
Last updated: 22-Sep-2015
Registration status:
Registered until expiry date.
Name servers:
ns1.netnames.net
ns2.netnames.net
ns5.netnames.net
ns6.netnames.net