Thanks for your e mail James.

The answer depends on the nature of the calls and whether they can be classed as a criminal offence (under I think it's under the Telecommunications Act). If they are really malicious rather than just a nuisance then you can ask the phone provider for relevant data as it would fall into the grounds of "detecting crime" under RIPA.

You would have to serve a notice on them under RIPA.There is an article on my site regarding accessing communications data.

However, surely the best way to deal with the calls is to report them to your telephone provider. Most have a malicious calls unit and they are usually pretty good. You may have to first report the matter to the police to get them to act though.

Hope this helps.

Regards