Sajid Javid has ordered HMRC to make no-deal planning its "absolute top priority" in the latest sign of his efforts to prepare for October 31.

The Chancellor has written to HMRC chief executive Sir Jon Thompson demanding action to support businesses and taxpayers and ensure systems are in place to "deliver a functioning regime" on Brexit day.

Sir Jon has earned a reputation for publicly spelling out the challenges posed by a no-deal scenario and has received death threats for "speaking truth unto power about Brexit".

Chancellor Sajid Javid and Home Secretary Priti Patel during their visit to Tilbury Docks, where he announced 2.1bn for no-deal Brexit preparation. Credit: PA

In a letter to Sir Jon, Mr Javid said: "HMRC must make no deal preparation their absolute top priority as the UK prepares to exit the European Union on 31st October 2019, with or without a deal."

He said HMRC must deliver "critical internal systems and staffing" to function on October 31, including the 5,000-plus additional staff required to support and handle the increase in businesses making customs declarations.

Mr Javid said customs officials must work with counterparts from the Treasury, Home Office, Department for Environment, Food and Rural Affairs and Border Force to deliver the "necessary changes to customs, tax and welfare arrangements in order to ensure a smooth exit and transition".

Prime Minister Boris Johnson has ramped up no-deal rhetoric. Credit: PA

In his instructions to Sir Jon, Mr Javid said he expected to receive "weekly delivery-focused updates from HMRC to ensure progress remains on track" in the run-up to October 31.

The Chancellor believes everyone in the Government must be prepared for a no-deal exit, including every arm of the Treasury.

It is the latest sign of Mr Javid's intention to mark a new era at the Treasury after taking over as chancellor from Philip Hammond, who remains strongly opposed to a no-deal Brexit.

Mr Javid's comments come after a leaked Goverment memo which stated what the consumer market could look like in an event of no-deal.

Sky reported the slide was prepared in the final weeks of Theresa May's tenure as prime minister.

The leaked slide Credit: Sam Coates/Sky News/PA

The slide, prepared for ministers, says the pound could fall in the first month while Northern Ireland may face law and order challenges.

Marked "official sensitive" and titled "What this could look like on the ground", it also warns that UK nationals in the European Union could lose access to services and residence rights within the first 24 hours.

A Government spokesman, in a statement on behalf of the HMRC, said: "HMRC has been preparing for Brexit every day since the referendum.

"HMRC has a system ready to handle customs declarations after Brexit, is rolling out a new Customs Declaration Service alongside this and has delivered new processes at the UK's borders.

"We've updated parliament on our progress regularly and continue to prioritise preparing the UK for leaving the EU on 31 October."