Aggressive Russian actions close to the UK and terrorism around the world has emphasised the importance of maintaining a strong Royal Navy, Defence Secretary Michael Fallon said as he cut the steel on a new patrol vessel.

Mr Fallon visited BAE's Govan shipyard in Glasgow as work began on the HMS Medway, and the new Prince Of Wales aircraft carrier approached its completion.

The US has urged European countries to do more to defend themselves against Russian aggression in Eastern Europe, and growing unrest in the Middle East sparking terrorist attacks in western European countries.

US President Barack Obama has expressed concern that budget cuts in the UK may see Britain drop below Nato's target of spending 2 per cent of GDP on the military.

Rear Admiral Henry Parker said he is "concerned" about money, but welcomed the UK Government's pledge to protect the equipment budget.

Mr Fallon said: "The US wants to see all of us in Europe doing more to defend ourselves, and modernising our armed forces is a key response to that.

"We have the fifth biggest defence budget in the world, the biggest in Europe, but the United States wants all European countries to do more to defend themselves with the rise of Russia and the aggression that we have seen in the east, and the very direct threat of Isil and instability in the Middle East, to the streets of London, Paris and Brussels.

"We face across the world terrorism, piracy, drug smuggling, so it's very important that we keep our Navy up.

"In recent months you have seen a more aggressive Russia sailing submarines and ships close to our coast, moving aircraft into our airspace, so it's very important that we continue to strengthen and modernise our defences. This ship today is very much part of that."

Admiral Parker said: "What we are seeing worldwide now is counter-terrorism threats that we may need to deal with at home.

"So in conjunction with other agencies in the Government, the Royal Navy sees that these ships will have a role in dealing with these wider threats to our security.

"We're always concerned about the money, but the important thing for me is that the Government's commitment to the equipment programme in defence has remained entirely intact.

"So we will continue with the assumptions that we have got and that will drive this programme.

"I am absolutely sure that we will be operating these ships for the next 30 to 40 years, and I'm pretty sure that we will need them replaced but that will be a decision for my grandson, let alone my son."

The SNP is reportedly seeking two seats on the Commons Defence Committee, in recognition of the geographical and technological importance of the UK defence industry in Scotland.

Mr Fallon said: "That's a matter for the House of Commons but it's for the SNP to argue its case.

"I hope they understand, though, that this investment today is an investment not just in Scotland but in the defence of the United Kingdom which the clear majority of the Scottish people voted for last autumn.

"This is a great day for Scotland. You have seen the steel cutting of the next new patrol vessel to be built here on the Clyde.

"Later this afternoon we will be debating the Scotland Bill giving new powers to the Scottish Parliament.

"So you're seeing political and defence investment in Scotland, which I think is important for the future and gives the clearest possible signal that we are all in this together as a United Kingdom."