The B.C. Liberals have failed again in their efforts to clamp down on third-party spending on advertising before an election.

The B.C. Court of Appeal has ruled amendments made by the Liberal government to the Election Act are not constitutionally sound because they limit freedom of political expression.

The government first tried to impose limits on political advertising in 2008 by halting any spending 60 days before an election.

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After the courts struck that down as unconstitutional, the government revised the law to 40 days and referred it back to the courts for approval.

In Thursday's ruling, Justice Peter Lowry says the definition of election advertising put forward by the government is too broad.

The court's ruling increases the likelihood that there will be no law preventing interest groups from spending what they like in the period before the May 2013 election.