"The prison was breached, over 100 very serious prisoners escaped", Sir Alan said. Further advisors are expected to arrive across the islands in the coming days.
Boris Johnson has spoken of Britain's "duty" to Caribbean islands hit by "hellish" Hurricane Irma on a visit to the devastated region. According to Duncan, 500,000 British nationals were in the hurricane's path.
Johnson flew immediately on a military flight to hard-hit Anguilla, and plans to visit the British Virgin Islands on Wednesday.
The Defence Secretary added that the French have military garrisons in their Caribbean overseas territories so already have troops in position.
UK Government will aid match public donations to the Red Cross appeal up to £3 million.
May also announced the government would be increasing the relief fund for British Overseas Territories left devastated by Irma from £12m to £32m.
The all-terrain vehicles have been stowed on HMS Ocean which is due to sail to the Caribbean today.
There were 420,000 British citizens in Florida either as residents or visitors, where Hurricane Irma also caused devastation.
SEE MORE: Do We Need A Hurricane Category 6? "We will support the mid to long term efforts on the ground and help provide support as those affected recover from the disaster". I am pleased to say that 48 hours later we have been able significantly to reinforce the Marines.
However Mr Johnson said that the hurricane has been "an unprecedented event, an unprecedented catastrophe" for the people who live in the part of the Caribbean which has been worst hit.
She said it was "alarming" that nearly a week had passed since the hurricane and Sir Alan was "still talking about the potential evacuation of British citizens".
Almost 40 of them are considered extremely risky, with fears that security on the island devastated by Hurricane Irma is extremely vulnerable, writes The Telegraph. The plan should include the possibility of more extreme weather "as the effects of climate change continue to grow", he said.