Pro-European voices must speak up "loudly and early" ahead of what will be a "very close run" referendum on the UK's EU membership, Scottish Conservative leader Ruth Davidson has said.

Ms Davidson wants the UK to stay in Europe but she supports David Cameron's decision to negotiate reforms and hold a "long overdue" vote on membership before the end of 2017.

The Tory leader set out her position on the vote in a speech in Brussels, stating that her own MSPs will be free to campaign on either side of the debate.

She said she supports the decision for UK Conservative Party resources and machinery not to be used for either campaign.

Ms Davidson has already ruled out the use of Scottish party machinery in the fight for either an "in" or "out" vote.

Speaking at the New Direction think-tank, she said: "Any individual within the Conservative Party should be free to campaign on any side of the debate that they want. My MSPs know that they have already been given just that freedom.

"But they will be doing that as individual MSPs. They are not part of the UK Government and, as for MPs, the Prime Minister has laid out his view.

"My experience of the Scottish referendum campaign is that cross-party campaigns - for all their internal tensions - can and do work, showing people that some issues can and do transcend the usual political knockabout.

"I think the one lesson I would urge those running the campaigns to consider is the import of voices from outside elected politics. People with practical experience and a considered view to help inform and explain the impact a decision either way would make.

"Above all, what we must avoid is a sense after the referendum that people have not had their fair say. As in the independence referendum, it is vital that a level playing field is created and that the match fairly played out."

She added: "So I support the decision taken yesterday that the UK party resource and machinery will not be used for either campaign, just as I ruled out - before the summer recess - the Scottish party machinery being used to such ends.

"Such fair play will be vital when - whatever the result - the country has to pull together after the vote has taken place.

"I also think it will be important for those of us on the pro-European argument to speak up loudly - and early."

Ms Davidson's intervention comes as David Cameron is to welcome French President Francois Hollande to Chequers as he steps up his diplomatic efforts to secure support for the UK's membership renegotiation.

Foreign Secretary Philip Hammond will also press the UK's case for reform in Brussels and Paris this week during efforts to push the issue back up the agenda.

Commenting on Ms Davidson's speech, SNP MSP Christina McKelvie said: "Before Ruth Davidson had even got to her feet, her pledge that she would make a positive case for EU membership had been exposed as nothing more than hollow words - as it was revealed that her own party won't even support her campaign.

"This 'neutrality pact' from Tory HQ barely conceals the bitter divides within the party over our EU membership. It is a severe blow to the credibility of both Ruth Davidson and David Cameron that they can't even carry their own party with them on such a vital issue. No wonder Ms Davidson left the country to make this speech."

Ukip MEP for Scotland David Coburn said: "Ruth Davidson's pro-EU speech in Brussels shows that the only anti-EU party in Scotland is Ukip.

"Scots opposed to the EU should vote for Ukip in the May Scottish parliamentary elections regardless of party. All the other parties support rule from Brussels, including the Tories, to a greater or lesser extent."