By Willie Rennie

Two weeks ago, a tweet from the Prime Minister signalled the start of the referendum on the UK’s place in Europe. I have called on all party leaders in Scotland to nail their colours to the mast. Over the next few months I will be campaigning fiercely for a strong Liberal Democrat team at the Holyrood elections. But where the opportunity presents itself, I will also work with people from all parties and none to make the case for Scotland and the rest of the UK remaining at the heart of Europe. I hope that Nicola Sturgeon, Ruth Davidson and Kezia Dugdale will join me.

The fragmentation of the campaign won't help. It is vital that those of us who believe that we are better off in the EU work together. I want all of us who want to see a vote to remain in the EU to stand united. This will be difficult in the midst of a Scottish Parliament election but it is hugely important.

I am lucky enough to lead a party that is clear in our support for the EU. If you look at the Conservatives, the difficulties that splits can cause are clear.

The official campaign has hardly begun but already we have seen the emergence of Tory in-fighting that would be familiar to anyone who watched the Conservatives pull themselves apart over Europe during the 1990s. Boris Johnson has joined Michael Gove and other senior members of his party in campaigning to leave.

In Scotland, dissent within the Conservative party may appear more muted but it is there. One MSP has already declared her intention to vote to leave. A newspaper survey of constituency associations found that a majority of Edinburgh Tories will vote to leave as well. Doubtless this pattern will be repeated in other parts of the country too.

I do not wish to be bogged down in the internal contradictions of a party that spent two years arguing the merits of remaining part of something bigger only to now claim exactly the opposite. That will not help persuade a single wavering voter that a remain vote is in the best interests of Scotland and the rest of the UK.

What is more concerning to me is that the Tories and the SNP have already shown a clear willingness to use the EU referendum as an opportunity to talk up the possibility of a second referendum on independence for Scotland.

The First Minister’s claim that a leave vote will inevitably lead to a second referendum is familiar. We heard it again in her speech in London this week. Claims that the SNP will lead a positive campaign are inevitably followed by dark warnings of the consequences of a vote to leave the EU.

There is constant talk of Scotland being pulled out of the EU against our will. Anyone familiar with the SNP’s brand of campaigning will recognise this divisive rhetoric.

Meanwhile, Scottish Tories desperate to avoid talking about their own EU splits have seized on this as an opportunity to keep focus on the last referendum instead of talking about Europe. The Tories and the SNP are two peas in a pod in this respect.

This approach has more to do with short-term electoral interests than the future of our country. The EU referendum is too important to be treated as a tool to foment new grievances or hark back to the independence debate.

People on both sides of Scotland’s constitutional argument recognise that the last two years have been hugely divisive for our country. For every positive story of a young person engaged in politics for the first time, we hear another about people falling out with friends and family over their referendum vote.

The last thing that Scotland needs is to return to a question that was settled decisively almost 18 months ago. That will not help rebuild bridges that were burned in the heat of the independence campaign.

The message to Ruth Davidson and Nicola Sturgeon is clear. They are talking about the wrong referendum. If they really want Scotland and the UK to remain in the EU they need to put narrow self-interest to one side and start acting like they do.

Ruth Davidson has the chance to put her position on the EU beyond doubt at her party conference today. She needs to take it.

Willie Rennie is leader of the Scottish Liberal Democrats.