As a whole, the nation WAS competitive - why? because we had a balanced and stable finances.
the 1970's period is unfortunate.
Opec strangled the world economy by restricting oil supply, it hurt us a great deal, and led, in error to people voting in thatcher.
Energy is key to economic growth, the rest are just symptoms.
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fundamentally, an hours work, is worth an hour - if a worker here is not competitive vs a labourer in a foreign land, then perhaps its just a fault of the currency markets and other features which act to make the playing field hilly - one of the many market failures we constantly deal with - So that justifies subsidy and tarrif barriers to correct for market failure.
http://www.bbc.co.uk/iplayer/episode/b00scpzn/The_Box_That_Changed_Britain/
Prior to 1970, if you imported from the far East, shipping costs were 30% of the product price.
By the time containerisation was done in 1984, its was less than 2%. In the UK, its cheaper to get goods from China to Felixstowe than it is to get them from Felixstowe to Manchester.
That alone removed the competitive advantage being local offered many workers. And there has been a lot of technology changes, like just in time stocking, that have similar effect. Those who rely on unskilled labour are at a permanent disadvantage. They have been for 40 or so years. If you consider that Google and others are now piloting driverless vehicles, you can expect another tranche of delivery men, truckers, taxi drivers and so on to be added to the uncompetitive group.
And no political change really affects that underlying fact. Socialism can't make up for the fact that we have huge amounts of surplus labour.