The navy will get its planned two new aircraft carriers at a cost of more than £5bn in a package of defence cuts agreed yesterday that will shape the future of Britain's armed forces for many years to come.

After weeks of intense debate centred around the carriers, the outcome of the government's long-awaited strategic defence and security review was agreed by senior ministers and military chiefs at a meeting of the national security council, chaired by David Cameron.

It agreed that the RAF will lose squadrons of fast jets and bases and the army will get rid of scores of large tanks and heavy artillery pieces. Last night the navy was said to be happy with the outcome, although it remained far from certain what and how many aircraft would fly from the carriers – and when.

The prime minister will announce the results of the review to parliament next Tuesday, the day before the government's comprehensive spending review.

The review's shadow was always hovering over a debate about Britain's future defence needs, which both government supporters and critics said was dominated by the Treasury.

To try and distance the security and defence review from Wednesday's package of cuts William Hague, the foreign secretary, or Liam Fox, the defence secretary, will publish a ministerial statement on Monday setting out what Downing Street calls "the strategic context" of the defence review.

The prime minister's spokesman would not officially comment on the national security council discussions, which lasted around an hour, saying only that "very good progress" had been made.

Fox is under pressure from the Treasury to address a £38bn overspend in the Ministry of Defence procurement budget over the next 10 years. The Treasury is demanding a further 10% in cuts in Fox's annual £37bn budget over the next spending period from 2011-15.

Last night the Telegraph reported that Air Chief Marshal Timothy Anderson, director general of the military aviation authority, told MPs the cuts would mean the UK "would be unable to respond effectively to a 9/11-style terrorist attack from the air".

In a rare move highlighting one of the new threats expected to be seized on by the government next week, the director of GCHQ, the government's electronic eavesdropping agency, warns today of the growing threat of cyber warfare. "There are over 20,000 malicious emails on government networks each month, 1,000 of which are deliberately targeting them," Iain Lobban said in a speech last night to the International Institute for Strategic Studies, but released only today.

Lobban also made it clear that GCHQ, which is based in Cheltenham, wants to recruit more staff able to protect computer systems from cyber attacks and to find out who is attacking.

"I … want to bang the drum publicly about the importance of technology and cyber skills so that we can sustain a flow of top-quality recruits into GCHQ and its industry partners," he said.

Lobban called for an aggressive approach to cyber attacks as he warned of the dangers of adopting the sort of defensive posture famously symbolised by France's Maginot line, which was meant to repel the Nazis.

"A 'Maginot line' approach to defence will not be sufficient of itself," he said. "'Patch and pray' will not be enough. At the national level, getting the rest of cyber – the more difficult 20% – right will involve new technology, new partnerships, and investment in the right people."

His speech echoes a warning last week by Fox of what he called the "battle for cyberspace". The defence secretary said this involves states, as he highlighted a cyber attack by Russia on Georgia.

"Russia's invasion of Georgia, with heavy armour, air strikes and ground troops – all very conventional – was augmented by a surgical cyber attack on the Georgian government and a sophisticated information operations campaign aimed at the Georgian people and the international community," Fox told a fringe meeting at the Tory conference.