Keir Starmer has promised to make Britain “battle-ready” as he unveiled a defence review designed to counter threats from countries such as Russia, which he warned directly threatened the UK every day.

Speaking from the BAE Systems shipyard at Govan, in Glasgow, the prime minister promised to spend billions more on weapons factories, drones and submarines – even if it meant raiding welfare or the aid budget once more to do so.

Amid an ongoing row over how the government will fund Starmer’s “ambition” to spend 3% of gross domestic product on defence in the next parliament, the prime minister argued defence had to be prioritised above other public services.

“[The defence review] is a blueprint to make Britain safer and stronger, a battle-ready, armour-clad nation with the strongest alliances and the most advanced capabilities,” Starmer said.

He added: “Russia is already menacing our skies and our waters, and threatening cyber-attacks, so this is a real threat we’re dealing with.”

The prime minister has promised to spend 2.5% of the country’s economic output on defence by 2027-28, with a further ambition to spend 3% at some point during the next parliament.

Asked what he would say to Scottish voters concerned about the government cutting benefits while increasing the defence budget, Starmer said: “I am absolutely clear in my priority is the safety and security of everybody in Scotland.”

The prime minister is facing a tricky byelection this week in the Scottish seat of Hamilton, where Labour was hoping to challenge the Scottish National party, but could end up coming third behind Reform UK.

Asked to rule out raiding the aid budget once more to pay for his post-2029 promises, Starmer added: “The best way to pay for an increase in any public spending is to grow our economy, and that is the focus when it comes to defence or any other spending.”

Speaking to the BBC earlier in the day, he said he would not set out in detail how he could pay for the 3% target.

“I am not, as the prime minister of a Labour government, going to make a commitment as to the precise date until I can be sure precisely where the money is coming from, how we can make good on that commitment, because I don’t believe in performative fantasy politics, and certainly not on defence and security,” Starmer told BBC Radio 4’s Today programme.

Pressed again on the date, he said: “We had a commitment for 2.5% by the end of this parliament. We pulled that right forward to 2027. We showed that when we say there’s a new era of the defence and [that] security of our country is our first priority – as it is – that we meant it. We take the same approach to 3%.

“But I’m not going to indulge in the fantasy politics of simply plucking dates from the air until I’m absolutely clear that I can sit here in an interview with you and tell you exactly how that’s going to work.”

The defence review will say Britain must be ready to fight a war in Europe or the Atlantic, though it is not expected to promise immediate increases in the size of the armed forces to deal with the threat.

The 130-page document will call for a move to “war-fighting readiness” to deter Russian aggression in Europe and increases in stockpiles of arms and support equipment, some of which may only last days in a crisis.

Questioned on whether this could involve, for example, British troops being sent to defend attacks on countries adjoining Russia, Starmer replied: “I very much hope not. And in order to make sure that that isn’t the case, we need to prepare. But we cannot ignore the threat that Russia poses.

“We’ve seen what’s happened in Ukraine just over three and a half, three years ago, those tanks rolled across a border, something I think all of us thought we wouldn’t really see in our lifetimes – the invasion of a European country. Russia has shown in recent weeks that it’s not serious about peace. We have to be ready.”

The review is not expected to contain any additional spending commitments. The defence secretary, John Healey, acknowledged on Sunday that any plans to increase the size of the British army, which is at its smallest for 300 years, would have to wait until after the next election.