OAP,
If the UK were to concentrate upon what you propose then we would effectively become another Ireland armed forces wise, with all of our resources devoted to the services who really effect and counter the only proper threat to the UK, that being from the actions of terrorist groups associated with extremism and lunatic individuals. As to the UK not having the budget to project it's own effective force, why not with the world's 5th largest defence budget and the largest in Europe stemming from the 5th largest economy in the world?
But don't worry, if you voted for Brexit then you are assisting in changing that!