Labour's shadow justice secretary Graeme Pearson, a former director of the Scottish Crime and Drug Enforcement Agency, said effective working by security agencies, such as MI5 and Special Branch, is easier as part of the UK.
But Allan Burnett, previously counter-terrorism coordinator with the Association of Chief Police Officers in Scotland, dismissed concerns, insisting an independent body could do better.
The exchange was sparked by a report, sponsored by Pearson, on security in Scotland, which features contributions from academics, civil servants, police officers and former intelligence officers.
It concludes that while Scotland has developed a distinct approach, it remains integrated with UK and global institutions. Pearson said the findings show there are real concerns about breaking up the UK.
"From my experience as a police officer for over 35 years, developing effective working relationships with colleagues across the UK is far easier because we are part of the UK. As the experts make clear, breaking up the UK could have direct impact on the ability of Scottish police officers to do their job."
Burnett, however, a director of intelligence at the old Strathclyde Police force, said: "UK security is a long way from being perfect. Multiple organisations fight for power and influence, and inappropriate UK Government interference is rife.
"There is a great opportunity for an independent Scotland, where cooperation is a reality and not just an aspiration, to do very much better."