Defence cuts mean Britain is no longer full military ally of America, ex-US Defense Secretary Robert Gates warns Britain does not have 'full spectrum capabilities', Robert Gates warns He 'laments' defence budget cuts on both sides of the Atlantic But ex-UK Defence Secretary Liam Fox insists Britain still pulling its weight David Cameron today hit back at claims defence cuts mean Britain is no longer a key full military partner to the United States. The Prime Minister dismissed the criticism from Robert Gates, America's former defense secretary, insisting Britain remains a 'first-class' military power. Mr Gates said the UK's ability to fight on land, sea or in the air has been undermined by moves to slash spending and troop numbers to fill a multi-billion pound blackhole in the defence budget. David Cameron rejected criticism from former US Defense Secretary Robert Gates who claimed UK defence cuts means Britain is no longer a full military ally of America The Government is planning major cuts to the Armed Forces. The Army is being cut from 102,000 to 82,000 over a number of years, with the 20,000 posts expected to be gone by 2020. Navy numbers are expected to fall by 6,000, while the RAF will lose 5,000 staff. Mr Gates, who served under presidents Barack Obama and George Bush, told BBC Radio 4's Today programme that naval cuts were particularly damaging, noting that for the first time since the First World War Britain does not have an operational aircraft carrier. He said: "What we have always been able to count upon on this side of the Atlantic was British forces had full spectrum capabilities very much along the same lines as our own forces that they could perform a variety of different missions. Former UK Defence Secretary Liam Fox rejected the idea that Britain is not pulling its weight With the fairly substantial reductions in defence spending in Great Britain, what we're finding is they won't have full spectrum capabilities and the ability to be able to be a full partner as they have been in the past. Because I lament our own defence cuts, I would say I also lament that reality in terms of Great Britain,' he told BBC Radio 4's Today programme. But Mr Cameron rejected the criticism. Speaking on a visit to the Crossrail project in central London, the Prime Minister said: 'I don't agree with him. I think he has got it wrong. We have the fourth largest defence budget anywhere in the world. We are investing in future capabilities. We are a first-class player in terms of defence and as long as I am Prime Minster that is the way it will stay. However Mr Gates' concerns echoed those of senior military staff in the UK. Last month General Sir Nicholas Houghton, the Chief of the Defence Staff, warned that manpower was increasingly seen as an "overhead," and that Britain was in danger of being left with hollowed out armed forces, with "exquisite" equipment but without the soldiers, sailors and airmen needed to man it. He told the Royal United Services Institute military think-tank that the Royal Navy was "perilously close" to its "critical mass" in terms of manpower. HoweverLiam Fox, who was Defence Secretary from 2010 when the coalition was formed until November 2011, dismissed the idea that Mr Gates" criticism would lead to "hurt pride" in the British military. I've sat beside him in a very large number of meetings over the years and I know him very well, and he's been a persistent critic, particularly of European-Nato countries who do not pull their weight.. who are spending 1 per cent of their GDP on defence. The UK need to remember when we did the defence review, we set out the fact that we'd be able to carry out an enduring stabilisation operation at brigade level - that's about 6,500 personnel - while conducting a complex non-enduring one of about 2,000 personnel plus a simple one at the same time. That is far more than any of our allies in Nato outside the US can do. So we're providing a broad range of capabilities. Labour's shadow defence secretary Vernon Coaker said: 'It should worry David Cameron that Britain's strongest ally has concerns about his Government's mishandling of defence.' Mr Fox also highlighted that the US is also cutting its spending on the military. The US is making substantial cuts of about $500bn to the Pentagon budget over this decade. America's the world's biggest economy with the world's biggest defence budget. We're the world's eighth biggest economy with the fourth biggest defence budget, so certainly we're pulling our weight on that and we're one of only four or five countries inside Nato to meet our 2 per cent GDP spend commitment. So I don't think we can be questioned on that. Countries in the West who want to be able to spend more on their security need to deal with their economic problems now. A Ministry of Defence spokesman said: 'Like the United States, the UK has had to take tough decisions on defence spending, but we still have the fourth largest defence budget in the world and the best-trained and best-equipped armed forces outside the US. Over the next decade, we plan to spend GBP160 billion on equipment, to ensure our armed forces retain their formidable range of cutting-edge capabilities and ability to project power across the globe, including by maintaining our major naval presence in the Gulf region. 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.