The government is facing a backlash from MPs for not joining an EU scheme to get extra ventilators during the coronavirus outbreak.
The bloc has said the UK can take part in the project, which will use the EU’s buying power to purchase more stock.
But a No 10 spokesman said the UK was “making [its] own efforts”.
Liberal Democrat MP Layla Moran accused the PM of putting “Brexit over breathing”.
The UK currently has 8,000 ventilators available and has placed orders for another 8,000 from existing manufacturers, but there are concerns about capacity in hospitals as the spread of the virus worsens.
Last week, the government put out a call for other British businesses to convert their factories to make the equipment, and has since signed a contract for 10,000 ventilators with Dyson.
But Boris Johnson’s spokesman confirmed the ventilators still needed to go through standards checks and would not be bought and distributed until that happened.