AN independent Scotland would be less safe and more vulnerable to a terrorist attack, William Hague will warn today.

Speaking in Edinburgh in his first major intervention in the debate, the Foreign Secretary will say Scots would have to "start again in world affairs" and face the cost of establishing new diplomatic and intelligence networks.

He will say he has met "bafflement anyone would try to break up a union that has been so resilient, so successful and so admired as ours" while travelling to about 70 countries in the past three years.

The Secretary of State will emphasise Scotland's membership of the world's sixth-largest economy, which is represented at the G7, G8 and G20 and has a permanent seat at the UN Security Council as well as an influential and growing diplomatic network.

In contrast, a Yes vote would bring "an uncertain future where Scots would have to face the inconvenience and tremendous burden of having to start again in world affairs, with a different passport for future generations, without that global network and enviable diplomatic position in the world and without automatic entry to Nato and the EU".

The Foreign Secretary will say the cost of creating new institutions would place an enormous burden on the taxpayer, taking years to develop the infrastructure and personnel needed to deal effectively with an array of threats.

He will argue the UK's intelligence services and armed forces, benefiting from significant economies of scale and years of institutional development, provide a high degree of security.

He will say: "So not only is Scotland safer in the UK but the UK is one of the world's leading nations in human rights, development and trade because we stand strongly together: a force for good in the world, with the ability to protect the interests of our citizens at home and abroad."

Mr Hague will point to the G8 summit as proof of the UK's seat at the top table of decision-makers.

He will declare: "The UK is not a passive observer. We are at the heart of global events. We help shape the world we live in and our voice matters and it is listened to."

He will also say the UK's international structures provide Britons with help and keeps them safe.

He will say: "When adventure turns to misadventure for UK nationals overseas, when there is a terrorist attack or a natural disaster, when criminals strike or British children are forced into marriage overseas, that is when we all feel the benefits of being able to turn to one of our missions in 267 posts in 154 countries and 12 territories worldwide.

"Scotland derives many benefits from being part of this global diplomatic network, instead of having to rely on fewer, smaller embassies which would take time and resources to establish."

The SNP's Angus Robertson said the test for Mr Hague would come if he mentioned issues like Trident, despite most Scots being opposed to it, the UK's role in the Iraq war, rendition flights or Britain's membership of the EU, the potential subject of a referendum.

He said: "Some 150 countries have become independent since 1945 and countries around the world understand the principle of being responsible for your own decisions. Independence offers us the opportunity to make Scotland's place in the world one that meets the aspirations of our people."