ACER has launched a quarterly report on REMIT, and one interesting nugget is that 30 cases of potential breaches of the regulation were being investigated at the end of 2014. The agency said 14 investigations were closed during 2014.
Potential REMIT breaches are investigated by national authorities rather than the agency, although ACER can coordinate cross-border cases. A national regulatory authority has not gone as far as pursuing a prosecution for a potential breach that I know of. I have been told some regulatory authorities are reluctant to be the first to prosecute, preferring instead to leave the first case to one of the bigger, and better-resourced authorities, although if a case turns out worth pursuing then presumably it would have to be.
Different countries have different sanctions for REMIT, with some introducing criminal sanctions and others civil. The UK is set to bring in criminal sanctions on 13 April. Its adoption will see those that breach the regulation sentenced to a maximum of two years in prison. The UK government will keep the possibility of making the maximum sentence similar to that of financial criminal offences, which have a seven-year maximum sentence, under review.
You can find the ACER report here.