Allan Burnett insisted security services could be "readily created" and traditional alliances easily maintained if Scots vote Yes next year.
His remarks come as figures close to the UK security establishment warn that SNP strategists have "naïvely" underestimated how much time and money it will take to create a secret police service.
Burnett was the old Strathclyde Police's head of intelligence and Scotland's counter-terrorism co-ordinator before retiring in 2010 with the rank of assistant chief constable, and endorsing the SNP.
He believes Scottish policing – with the biggest Special Branch outside London and substantial existing capacity to deal with terrorists and organised crime – already has the basis of a strong MI5-style domestic security service.
He has accused UK authorities of refusing to discuss post-independence intelligence sharing in order "to cut off debate" on the issue.
Burnett said: "Their studied intention is to fill the discussion gap they have created with scurrilous scaremongering. 'The Americans won't share intelligence with you', 'you're leaving yourselves open to terrorist attack.' The truth is that an independent Scotland would face less of a threat, intelligence institutions will be readily created, and allies will remain allies."
Burnett's views on a domestic security service chime with those of Peter Jackson, an international expert in the creation of modern intelligence services.
Writing in today's Sunday Herald, right, Canadian-born Jackson, professor of security at Glasgow University, said Special Branch would form a "suitable nucleus" of any Scottish MI5. And he said Scotland, like Canada and Nordic states, would probably forego an MI6-style overseas spy network, instead relying on pooled intelligence or diplomatic open sources.
Jackson agrees with Deputy First Minister Nicola Sturgeon, who has argued that espionage services in the rest of the UK would have an interest in sharing intelligence with Scotland.
Burnett said: "The rumour that allies will shun us comes from the same box of tricks as the European Union exclusion nonsense.
"We occupy a strategically vital position in the North Atlantic. Our friends, including those south of the Border, will want us as allies as much as we want them."
But Labour peer Meta Ramsay disagrees. The former senior MI6 officer believes English, American and other overseas services would take some time to trust their new Scottish partners.
She said: "Do not assume that everybody – even nice Nordic and other countries, and even the ones near to you – will just give you all their stuff because you're Scotland and they quite like you."
Agencies don't share intelligence with those they like, she stressed, they share with those they trust and only when it is in their own interests to do so.
Ramsay – a Glasgow University-trained Russian expert – describes SNP rhetoric on intelligence as "extremely naïve".
She said: "They are talking about a world about which they obviously do not know - it is not going to be as simple as they think."
Ramsay said there are countries which get by with only a domestic security service, such as Finland and Sweden, where she served during the Cold War.
But she also disagrees on how easy it would be to create a Nordic-style domestic security service.
She said: "There seems to be an assumption, which I think is wrong, that Special Branch can be transformed by waving a magic wand into a security service. In my opinion the two things are not the same."