Former Nato secretary general Lord Robertson has called for a large increase in UK defence spending.
But he also told BBC Scotland that defence cash also had to be spent more wisely in the future.
Lord Robertson, a former UK defence secretary, argued that GDP spending in the area could rise to 3%.
At 2.2%, UK defence spending is already above the Nato European average, and the budget is set to increase to ?33bn in 2007/08 from ?32bn in 2006/07.
Outside the United States, no country spends more on defence than the UK.
Lord Robertson told BBC Scotland's Politics Show that future generations had to be given the guarantee of safety currently enjoyed by the public.
"I'm one of those who believes that a country has got to invest in defence and I think 3% of gross domestic product is a fair calculation to make," he said.
Lord Robertson went on: "If we're going to persuade the new chancellor and the present prime minister to spend more on defence - or even get the opposition to commit more money for defence - then all of us have got to make the case in the general population for saying a bigger share of the national cake needs to go to defence rather than education, health, housing - which are infinitely more popular among the voters."
Budget increases, he also warned, had to come hand-in-hand with decisions on how the cash was spent.
"In all of Europe, we spend a lot of money on defence," he added.
"Huge amounts of money are spent on soldiers who can't be mobilised, on tanks that will never move, on anti-submarine warfare assets against an enemy that doesn't have any submarines."
Lord Robertson has also moved to defend Prime Minister Gordon Brown's record on the military, saying he had been "tremendously generous".
The MoD has argued that the defence settlement allowed investment in world-class equipment for the armed forces, while driving through efficiency savings to ensure money was well spent.