I think they will get away with making the calls until enough victims report them for fraud/attempted fraud.
Interesting that the calls are starting to come from within UK (Sheffield) might be copycats or relatives of the India lot that got shut down guardian.co.uk/technology/2012/oct/04/ftc-cracks-down-tech-support-scam
"As explained by the Guardian in 2010, the scams used "boiler room" tactics, dialling through phone books for English-speaking countries. People who answered the phone were told the call came from Microsoft or their internet service provider"
"..Though the FTC said it could not put a figure on how many people had been scammed, or how much they had lost, Microsoft – which has been working with the commission for the past two years to try to catch the criminals..."