In Ireland, for example, there is a form of proportional representation that has been there since the creation of the Irish Free State, and Éamon de Valera tried to get rid of it.
There are a number of problems with proportional systems, such as with the European Parliament, where people don’t know who their MEPs are and just voting for regional lists. I doubt whether many people know who the MEPs are for Scotland – and that illustrates one of the problems with proportional systems.
A big question is who decides who’s on the list that we vote for and the answer is that it’s the parties that draw them up.
Another problem is what do you do about thresholds – because unless there is a threshold, anyone can get elected, which is what happens in Israel. However, if you move towards a threshold, that system then starts to become less proportionate.
Yet another example is Germany, where there is a proportional system and the centre party, the Free Democrats, has been in power for almost three-quarters of the period since the last world war on just 6 to 8 per cent of the vote.
Closer to home, we can look at the example of the Tory-Lib Dem coalition government and, while we don’t have PR for Westminster, we can ask how many people actually voted for that two-party coalition, which was agreed in a post-election deal.
If we’re looking at other electoral systems, we can’t just say: “Let’s stop the SNP and get a new system.” The whole thing needs to be looked at very carefully.
If we were to go down the route of having just lists for elections, then there’s a danger that you would no longer have people from different wings of parties in parliament, but people who were clones of parties.
There are, of course, issues about the role of the SNP at Holyrood, having such control over so many aspects of political life.
The Presiding Officer should always be from a different party to the one in power and there should be a quota for having a certain number of opposition MSPs as heads of committees.
One thing we need to remember during this talk about the Scottish Parliament, is that Margaret Thatcher’s highest share of the vote was 43 per cent, yet she had majorities of more than 100.
We could say this is wrong, but there are very important questions about proportional electoral systems.
• Trevor Salmon is professor of politics at the University of Aberdeen.