The Royal Navy's second new aircraft carrier, the Prince of Wales, is to be brought into service, rather than sold off or mothballed, Prime Minister David Cameron has announced.

The announcement came as members of the 28-nation Nato alliance sealed a pledge to reverse declining trends for defence budgets and to move towards meeting the target of spending 2 per cent of GDP over the next decade.

The future of the Prince of Wales, part of which is built in Hampshire, had been in question after the 2010 strategic defence review suggested it could be mothballed or sold to save money.

Mr Cameron said at a press conference at the conclusion of the two-day Nato summit in south Wales: ''This will ensure that we will always have one carrier available, 100% of the time.

''They are an investment in British security, British prosperity and our place in the world, transforming our ability to project power globally, whether independently or with our allies.''

A section of the carrier left BAE Systems shipyard in Portsmouth in August to be assembled in Rosyth in Scotland.

It was the yard's last order, ending hundreds of years of shipbuilding in Hampshire. Future surface work will be carried out in Glasgow yards.