The Ministry of Defence has admitted a serious breach of security - after two anti-nuclear protesters broke into Devonport naval base.

An MoD spokesperson said an "urgent and thorough" review of security was underway.

The two protesters claimed on Monday that they got on board the nuclear submarine HMS Vanguard without any resistance.

Since 11 September last year security at Devonport has been at its highest ever level, making this incident is an embarrassment for the MoD.

Pair bailed

The MoD says no damage was done to HMS Vanguard.

We just walked in all the way. It was really surprising, and worrying

Petter Joelson

But Devonport MP David Jamieson says he is very disturbed at the news, and is keeping in touch with the base's commodore throughout the enquiry.

Two people have appeared in Plymouth magistrates court charged with causing criminal damage at the base.

Petter Joelson from Sweden and Elisa Silvennoinen from Finland were given conditional bail before their pre-trial hearing next month.

Petter Joelson: Defiant

Speaking outside the court after the hearing the two activists, who support the protest group Trident Ploughshares, described the ease with which they entered the naval base.

"We walked inside the base and didn't see anybody.

"We got on to the nuclear submarine and walked around it first and then pushed the fire alarm," said Ms Silvennoinen.

"We have got a trial and that is a victory for us."

Mr Joelson said: "We just walked in all the way. It was really surprising, and worrying.

"But we are not here to make a point about security at the base. We are here to make the point that they have nuclear submarines."

A sit-down protest is broken up by police

The pair said they entered the base wearing ordinary clothing. They would not reveal where their point of entry was, or how they by-passed the security system.

Seven women protesters were arrested outside the Albert Gate of the base on Monday.

The women, who were arrested for obstruction, are being questioned by police.

HMS Vanguard arrived at Devonport in February this year for a two-year refit and refuelling.

It is the first of the Vanguard class submarines to be refitted at the naval base and is one of seven nuclear-powered submarines based there.