The threat from Philip Hammond and other ministers on Wednesday as they sought to explain the decision by BAE Systems to slash 1,800 shipyard jobs was pretty explicit.

Vote for independence and Scotland will not get any new shipbuilding orders from the Ministry of Defence. Vote to stay in the existing UK and Scotland will be the only British nation making warships. England will make none.

The defence secretary's message follows close on a paper by the Home office that is breathtaking in its arrogance - and if it is to be taken seriously, is astonishingly irresponsible.

"Scotland analysis: Security" is the latest in a series of papers put out by Whitehall departments on the disasters that would befall Scotland, and the dangers to England, if Scotland voted for independence in next year's referendum.

Taken at face value, it suggests that MI5 in a UK of Northern Ireland, England, and Wales, would not share important intelligence with an independent Scotland.

Whitehall – ironically, perhaps given the Conservative party's hostility to the EU – has already suggested an independent Scotland would not necessarily be welcomed into the EU or Nato. This despite Scotland's strategically important geographical position, close to important sea lanes and airspace.

The Home Office paper also includes tendentious arguments suggesting that one of the problems would be the lack of accountability of new Scottish security and intelligence agencies.

As a "separate state", Scotland could not "share" the UK's security and intelligence agencies "for reasons of sovereignty and democratic accountability", it says. "They would instead continue to operate in the national interest of the continuing UK".

It adds: "The UK could not share secret intelligence with an independent Scottish state that had been passed to it by another country without the originator's consent."

The Home Office paper continues: "It takes time to build this trust and confidence. Other states would only share with an independent Scottish state what it was in their own interests to share."

In international intelligence partnerships, most notably the "Five-Eyes" arrangement between UK, US, Australia, Canada and New Zealand, "each partner makes a substantial contribution in return for the benefits they receive". the Home Office notes. It goes on: "There would be no automatic right of entry to the 'Five-Eyes' community for an independent Scottish state....Entry is by invitation only."

It is all a "matter of trust and confidence, which would take time to build up – not only with the continuing UK but with other intelligence agencies around the world."

The Home Office makes Scotland seem as though it is just coming out of the backwoods of an unknown continent.