A former chief of defence staff warned tonight that Britain's armed forces were "not good enough" to deal with threats facing the world today.
Lord Richards of Herstmonceux said the biggest threat confronting the free world today was that posed by militant Jihadism.
In his maiden Lords speech, the independent crossbench peer called for a rise in defence spending and warned that without it, the effectiveness of the armed forces would inevitably deteriorate further.
Ignoring the convention that maiden speeches are meant not to be controversial, Lord Richards said: "Are our armed forces fit or in a fit state to play their role in dealing with these and other risks to our way of life.
"The answer must be that it's not good enough but it's some consolation that it's better than any other allied nation except the US."
Lord Richards, who was chief of defence staff until last year, said al l states were equally vulnerable to the threat from militiant Jihadism and they should "cohere to confront this threat with the adoption of a multi-dimensional strategy".
He told peers the struggle would be generational and political leaders must stop seeking "short term tactical solutions".
There must be a "containment strategy" so that once the periphery was stabilised "one would work progressively to recover areas that had fallen under the Jihadist yoke".
A key part of the strategy must be to honour commitments made at Nato summits in Lisbon and Chicago to support the Afghan people after the allies withdrew from a combat role at the end of this year.
He added: "Routine defence spending post 2015 must increase as a minimum to 2% of GDP.
"If not - given the mathematics that seem stubbornly to govern defence expenditure - the size and effectiveness of the armed forces will inevitably deteriorate further."
Given the highly unstable world "the brave experiment" to increase the army reserve must either soon be proved to work or a new solution found.
Lord Richards said it was vital that Britain's allies should shoulder more of the burden of security and warned ministers against breaking the "societal consensus" by failing to look after servicemen and women properly.
His comments came as the Government faced a withering barrage of criticism from former defence chiefs in a debate on the armed forces.
Former chief of the naval staff Admiral Lord West of Spithead warned the armed forces are being cut "into the bone". S pending cuts had put them on a "knife-edge" and without an increase "we are on the road to disaster".
The Labour former security and counter-terrorism minister said it was a "national disgrace" that Britain now had only 19 frigates and destroyers.
Former chief of the defence staff Lord Stirrup also warned that the level of defence spending was now "dangerously low".
Lord Stirrup, an independent crossbench peer, said: "We have allowed ourselves and Nato to grow weaker over the past few years.
"Risks and uncertainties are greater when we are weaker than when we are stronger. We need to be stronger if we want to be more secure."
He said Britain would not be able to meet all the challenges through "soft power" alone.
"We will need the capabilities of our armed forces, capabilities that we have progressively weakened in the name of financial retrenchment."
But defence minister Lord Astor of Hever insisted that, despite spending cuts, the Government had retained the capacity to protect the nation whatever the future may hold.
While acknowledging growing tensions in Iraq, Syria and Ukraine, Lord Astor said Britain's defence budget was still the biggest in the EU and its forces were the best trained and equipped outside the US.
Lord West said the price of "unrelenting operational tempo" on a navy with too few ships and too many tasks had led to lack of time for basic maintenance.
"Apparently some warships have had to be towed back to Britain after breaking down at sea because there's insufficient funding for maintenance and spares."
He said there was also pressure on navy personnel who had been "squeezed too much and stretched too thin".
Defence spending was "balanced on a knife edge" despite Britain being probably the sixth richest nation in the world.
Lord Stirrup warned that the global threats to security were many and serious. He said Britain should be doing all it could to prevent a "slide into a full blow Sunni-Shia war," which seemed to be very much in prospect at the moment
Lord Stirrup told peers: "The Government should face up to its responsibilities by delivering the necessary real-terms increases in the defence budget over the second half of this decade."
Lord Dannatt, a former head of the Army, warned that the effect of defence cuts was that the UK would now no longer be able to fight two simultaneous wars as they had in Iraq and Afghanistan.
He said the 2010 review had been produced "in response to the national financial situation and in recognition of the inherited overdraft in defence", but had "reduced defence spending, reduced our defence capability and has produced smaller - not smaller and better, just smaller - armed forces".
He added: "The international security situation as we approach the next defence review 2015 looks considerably more challenging than it did in 2010. Cutting defence spending any further would send all the wrong messages - to the Kremlin, to al Qaida, and those who do not share our British values.
"A modest increase in defence expenditure would signal that the UK still took its international responsibilities seriously and reassure both our Nato partners and our principal ally the United States."
Another former chief of defence staff, Lord Boyce, joined the assault on the Government over the strength of the armed forces.
The independent crossbench peer said the armed forces had a key role to play in an unstable world.
"But I have a serious concern that they aren't sufficiently resourced to do so particularly after the steady erosion of military capability over the last four years."
Lord Boyce said it was simply not good enough for ministers to say Britain had one of the world's largest defence budgets, when it wasn't even in the top six.
If the country was to meet the Government's aspirations and the armed forces were to play their part in that, "we must be aiming for something better than 2% of GDP" on defence spending.
The current frigate and destroyer force was "lamentably insufficient for a nation with global aspirations", he said.
A Ministry of Defence spokesman commented: "Tough decisions had to be taken to deal with the budget deficit left in defence but the UK remains the biggest defence economy in Europe and the second largest in Nato that spends above the target of 2% of GDP on defence.
"The Royal Navy's ability to project power and influence around the globe is evident with deployments of vessels to assist in the search for the missing Malaysian airliner; a Helicopter Carrier and Destroyer following the typhoon in the Philippines; while taking part in operations in counter-piracy, counter-narcotics and safeguarding chemical weapons being removed form Syria. All this is being carried out while maintaining a large Naval presence in the Gulf, while naval vessels are also defending the Falkland Islands and maintaining our continuous-at-sea deterrent.
"Construction of the first new Aircraft Carrier, the largest ship the Royal Navy has ever operated, is almost complete and the Navy will also operate state-of-the-art Type 45 Destroyers, new Type-26 Frigates, and seven new Astute Class submarines."
Another former chief of defence staff and independent peer Lord Craig of Radley questioned whether defence plans over the next six years were "realistic or realiseable" given current funding projections.
Far from increasing the defence budget references to further belt tightening seemed to indicate that more cuts were in the Chancellor's mind.
He said the next defence review must clarify Britain's role in the world and whether ministers wanted to remain in the forefront of alliance defence efforts.
Lord Craig warned there were few if any "quick fixes" in defence capability and if Britain wished to retain its place in the world now was the time to invest in capability and service numbers
For the Opposition, Lord Rosser said that since the defence planning assumptions of 2010 the intended size of the regular army had been cut by a further 11,500.
"A deliberately untested and unassessed objective of a projected increase in the size of our reserve army has fallen well behind schedule."
He said: "The conclusion must be that at the very best, the Government, through their own actions have placed the ability of our armed forces to deliver the defence outputs the Government itself set out in 2010, in jeopardy.
"To try to maintain otherwise in the light of the further reductions in the strength of our regular forces and the failure to achieve the required recruitment levels for the army reserve force without making any change in the planning assumptions lacks real credibility."
Winding-up for the Government, Lord Astor paid tribute to Lord Richards' "outstanding" maiden speech.
He told him: "We have routinely met and exceeded 2% of GDP since 2010 even allowing for urgent operational requirements.
"We expect to meet 2% until 2015-16. After that will be a matter for the next spending review."
The minister acknowledged that increasing the reserve from 19,000 to 30,000 would not happen overnight but said the coalition was confident of delivering the "reinvigorated" reserves by 2018-19 and investing £1.8 billion in better training and equipment.
"I can assure the House that for the first time since 1996 that total strength of reserve forces has risen to 22,480 - that's up 470 since January."