Ireland will decide as early as March 8 whether to put security checks at the border and increase fishery patrols in the Irish Sea, we have learned.

As preparations ramp up for the possibility of a no-deal Brexit, ministers have been told that many Irish companies will be putting staff on protective notice, we can also reveal.

On March 8 — when the Cabinet holds the last of three meetings aimed at saving the financial services, the agri-sector, fisheries and defence — the Government will begin distributing millions of euro in State aid.

Although Britain is not scheduled to crash out of the EU until March 29, in the words of one minister, ‘certain actions cannot be taken overnight’.

The Cabinet is to meet on March 4, 5 and 8 to decide which industries should get financial assistance from the State.

There will be a dinner for all ministers in Government Buildings on Monday, March 4, where, over the beef and potato gratin, the discussion will be Brexit, according to ministers. Then on Tuesday, March 5, and Friday, March 8, there will be special Cabinet meetings dedicated to Brexit planning.

If British Prime Minister Theresa May has not secured either a deal or a deferment for Brexit, Ireland will have to move on a no-deal basis. Ministers were informed of this timetable at Tuesday’s Cabinet meeting.

They were also given an in-depth ‘cataclysmic’ presentation by Government Secretary General Martin Fraser on the potential effects of a no-deal Brexit on Ireland. It is understood the agriculture and fisheries sectors were cited as examples of the industries most at risk, and ministers will also have to consider the impact of a hard Brexit on the financial markets.

One minister present said: ‘It was shocking stuff; I looked around the table and some of my colleagues were ashen-faced.’

The decisions that will be taken at the meetings will include:

Choosing the companies and sectors that require State aid — the Government expects large companies to put staff on protective notice at this point;

Establishing border animal and agri-food checks;

Establishing hugely increased fisheries protections in the Irish Sea;

Setting up complex financial services facilities to establish Britain as a ‘third country’;

Asking the Garda Commissioner to decide if he needs the support of the Army to guard the border.

All of these measures would take at least three weeks to arrange. A Cabinet minister told Extra.ie last night: ‘March 8 is the time that — if nothing happens to change Britain’s position — Ireland will take the decisions it needs to take for a no-deal Brexit. You don’t wait until it happens,’ he said. ‘If a company is going to be in a bad way in three weeks, you don’t wait for a no-deal Brexit — you take the intervention first.

‘There is a serious worry about the economy. There is a genuine worry about the impact of Brexit.’

The Government understands that even multinationals are going to put staff on protective notice. It produced its Brexit Omnibus Bill on Friday, which deals with changes to legislation needed in the event of Britain leaving the EU without an agreement.

‘The Omnibus Bill deals with bureaucracy around the payment of pensions in both states and that kind of thing,’ said a minister. ‘On the other hand, March 8 is about paying State money to companies, about the Army, installing border checks, about putting more fishery patrols on the sea — it’s scary stuff,’ added the minister.

The Cabinet was told that one industry that could be hit immediately is fisheries, said the minister. ‘There were words used at Cabinet like “cod wars” — and that from March 29 our boats aren’t allowed in their waters,’ the minister added ‘Financial markets, financial services, contracts… all of those have to be prepared,’ he said.

‘The financial sectors in Ireland and Britain are very much intertwined.’ The Department of Defence is prepared to let Garda Commissioner Drew Harris decide if he wants the Army deployed to support gardaí at the border.