A campaign to have MSPs elected by the same mechanism as councillors was launched yesterday by the Scottish Liberal Democrats.

Party leader Nicol Stephen lodged a motion in the Scottish Parliament calling on Westminster to introduce the single transferable vote, or STV, in time for the next Holyrood election in 2011, while his party colleague Jo Swinson tabled a similar motion in London.

Mr Stephen said: "Since we are now using STV to elect Scotland's councils it makes sense to use the same system to elect the Scottish Parliament. I welcome the Electoral Commission's decision to appoint an independent investigator to look into what went wrong in this month's Scottish Parliament elections. How-ever, it will take a great deal more than an Electoral Commission investigation to restore the public's trust in our democratic process.

"This month's local government elections have finally quashed the argument that STV is too complicated for voters to understand. With a much smaller total of rejected ballot papers in the council elections than in the Scottish Parliament elections, it is clear that having the same electoral system for both elections would have reduced significantly the problems we saw across Scotland."

Jo Swinson, the LibDem Scottish affairs spokesman at Westminster, added: "This government has already overseen the implementation of successful STV elections for the Northern Ireland Assembly. We have also seen all 32 Scottish local authorities successfully elected by STV. Now is the time to introduce STV elections for the Scottish Parliament. I have tabled a Bill in the House of Commons which will give the government an opportunity to amend the Scotland Act to this end."

The Electoral Reform Society will today launch a report proclaiming the success of the STV system for this month's council election.

A spokeswoman said: "The way voters coped with the council system seems to have been rather better than how they coped with the Scottish Parliament, so voters seem to have taken to the STV system ... we had only 2% of spoils in the council vote and 75% of the voters felt able to exercise more than one preference."