Big brands can be sensitive over any other business having a very similar website to them or one of the same name with a different extension.
E,g the Tesco supermarket website is at www.tesco.com but they also own tesco.co.uk, tesco.biz, tesco.uk and more.
The main reason for this is to avoid fraudsters trying to catch out people attempting to get to the genuine Tesco website.
Smaller companies are likely not so bothered about other people having similar domain names, but everyone wants to avoid fraudsters conning their customers of course.
Dnsuk.org send out vast numbers of emails to businesses, with a detailed story about how someone has asked them to register yourdomainname.net (I.e. whatever your domain name is) but that they have to give you first option on that domain name.
This is lies.
They want payment of £199.50 plus VAT to protect the domain name for 10 years by redirecting any traffic to that domain to yours instead.
If you actually wanted to buy yourdomainname.net it would cost much less than the amount dnsuk.org charge and there is no reason to pick 10 years.
Dnsuk.org may intend to disappear in a short time after gathering as much money as possible – that way the 10 year figure makes sense for them.
Do not be conned – if you want extra domain names then buy them through your hosting provider and certainly ignore such lying emails from dnsuk.,org
If you have any experiences with scammers, spammers or time-waster do let me know, by email.