New European laws banning spam e-mails have come into force.
It is now a criminal offence to send unsolicited commercial e-mails or text messages unless the recipient has agreed in advance to receive them.
Firms that continue to send spam face hefty fines and, in certain circumstances, can be sued by the recipients, under the new EU regulations.
The Government described the law as a "step in the right direction" in the fight against the millions of unwanted messages that clog up servers around the country.
But junk mail is expected to continue to deluge -accounts as most of it originates from outside the EU.
Firms using tracking devices such as cookies on their web sites will also have to tell users and provide an opportunity to reject them.
Companies or individuals that break the laws can be reported to the office of the information commissioner, which has powers to take them to the courts.
In the first instance, magistrates can levy fines of up to £5,000 sterling. The organisation can also be referred up to trial by jury, where there is no limit to fines.
Businesses that have relationships with their customers are exempt from the new laws, in an attempt to ensure that business-to-business e-marketing is not affected.
Spam now accounts for an estimated 50 per cent of global email traffic, compared with 8 per cent two years ago.