At the start of the year one in every 199 UK e-mails was spam, MessageLabs reported. By June the figure was one in 36 and in November it was standing at one in eight.
"Spam has the ability to severely compromise UK business productivity and these new statistics bear that out," said Mark Sunner, chief technical officer at MessageLabs.
The dramatic increase in UK spamming mirrors the pattern of the US, according to Matt Sergeant, senior anti-spam technologist at MessageLabs.
In the US, one in 37 e-mails was classified as spam in January, rising to one in three during November. "Unfortunately we are likely to be six months behind the US as we follow their Internet trends," Sergeant noted.
Sergeant attributed the increase in spam to the easy availability of "$20 CDs listing five million e-mail addresses and the increase in broadband services".
He added that insecure always-on connections also increased the likelihood of spam attacks.
The fastest growing source of spam is the "Nigerian scam", or "491 scam", according to MessageLabs. It asks for help in transferring large sums of money out of Nigeria, with bogus promises of financial rewards.
IT departments not only have to deal with pressure on networks and storage caused by spam, they also have "a duty to protect employees from fraudulent scams", said Sergeant.