Newly-released UK Government files have revealed former Prime Minister Margaret Thatcher's anger at a major military security breach which took place during her time in government.

The files show that Mrs Thatcher was livid after she was informed that three anti-nuclear demonstrators managed to board the nuclear-armed HMS Repulse.

After a major review of security at the base, sentries were instructed to shoot intruders on site if they were seen to offer any threat to the submarines or their nuclear payloads.

On October 10 1988, the Ministry of Defence (MoD) contacted No 10 to inform them that three men had forced their way on to Repulse after cutting through the Faslane perimeter fence.

There were suggestions that the intruders had managed to spray anti-nuclear graffiti in the control room before being overpowered by the crew.

Another female protester was also picked up near a different submarine, HMS Resolution, having apparently swum across the loch in the darkness wearing only a swimsuit.

Mrs Thatcher said in regard to the incident, in a hastily scrawled handwritten note:

"I am utterly horrified. Examples of slackness in sensitive matters keep coming to light. I must have an urgent report. We could have been put in grave danger."

Her foreign policy adviser, Charles Powell said at the time:

"Had they been armed terrorists; the consequences would have been incalculable."

The spot where the protestors had cut the perimeter fence would normally have been protected by coils of barbed wire, but due to engineering works they had been removed.

It was also discovered that the alarm system had been deactivated in the police control room.  

The group were able to take advantage of the presence of builders' cabins and construction equipment to move through the base unseen.

And whilst an MoD police patrol might have found them, they were on a tea break at the time.

There were also only three Royal Marine sentries on duty when there should have been four, and some floodlights were defective.

It was only when the protesters reached the control room that they were finally apprehended.

The inquiry report concluded they may never have intended to board a submarine and merely breached the perimeter fence as a diversion for the woman swimmer, who had an aerosol to spray anti-nuclear slogans on the dock.

As a result of the inquiry, 10 military personnel and three senior MoD Police officers were facing disciplinary proceedings, the PM was informed.

As well as this, a statement was given saying:

"The rules of engagement governing the armed guards on the Polaris jetties have been amended, with the agreement of the Law Officers, to make clear that they may, as a last resort, open fire to prevent a perceived threat of sabotage not only to nuclear warheads but also to the submarine." 

MORE - Records Reveal Thatcher Government Tensions