Simon Stevens said plans will "crystalise later this autumn when it's clear what the UK's position will be"
The boss of England's National Health Service (NHS) has said 'significant planning' is under way to prepare for a potential 'no-deal' Brexit.
Millions of packs of medicine, along with other essential medical supplies such as blood plasma, come into the UK from the EU every month.
NHS England chief Simon Stevens this morning told BBC's Andrew Marr Show: "There is immediate planning which the health department and other parts of government are undertaking around securing medicine supplies and equipment under different scenarios.
"That will obviously crystalise later this autumn when it's clear what the UK's position will be."
He added: "There is now significant planning going on around all the scenarios, including these medical supply scenarios."
He stressed that ensuring medical supplies continue as normal should be 'top of the list' of priorities in the event of the UK crashing out of the EU without a deal.
Speaking on the same show, the UK's Local Government Minister James Brokenshire acknowledged the government was preparing for 'all eventualities'.
However, he insisted: "The focus must be on actually getting that deal - getting that positive deal for our future.
"Of course, we must be prepared... and we will be."
On Friday, EU leaders met in Brussels to assess the 'state of play' in Brexit negotiations ahead of an October deadline for a deal - and they quickly confirmed 'no substantial progress' had been made regarding a backstop agreement for the Irish border.
European Council President Donald Tusk warned Mrs May that it was "the last call to lay the cards on the table."
Details of the British government's Brexit plans are are due to be finalised at a special meeting of cabinet ministers at Prime Minister Theresa May’s Chequers country retreat on Friday.
They are then set to publish a 'white paper' outlining what British officials expect the future relationship between the UK and the EU to look like.
Leo Varadkar has said a 'no-deal' Brexit is 'unlikely but possible' - saying Ireland will have to start preparing ports and airports for a worst-case scenario.