The Electoral Commission informs me that police forces are not obliged to report allegations of electoral malpractice to the Commission. Since 2008, however, the Commission has worked with police forces to establish a mechanism for collating information about cases of alleged electoral malpractice reported to the police.
In 2008, police forces reported 103 cases involving a total of 476 allegations of electoral malpractice in England and Wales; there were no elections in Scotland. In 2009, police forces reported 48 cases involving a total of 107 allegations of electoral malpractice in Great Britain.
The Commission has published its analysis of these cases, including the outcome of investigations and prosecutions where relevant. Copies of its reports for 2008 and 2009 have been placed in the Library.