The Health Secretary's promise that 100,000 people a day would be tested for coronavirus has been criticised as "arbitrary" and "irrational" by Downing Street sources.

In a sign that senior Whitehall figures are distancing themselves from the target – due to be met by the end of April – a Number 10 insider said Matt Hancock's pledge threatens to "come back and bite him".

The latest official figures show that just 19,316 tests were carried out in the 24 hours to 9am on Monday, while the most recent total testing capacity dropped by 2,000 to 36,000.

Sources say there is not the demand among NHS workers to meet the 100,000 target, and that widespread testing is most critical earlier in an outbreak and once lockdown measures have been relaxed.

On Monday, Wales announced that it was abandoning its own daily target of 5,000 tests of key workers each day because it was unachievable.

The Downing Street source said: "The problem is with this arbitrary target. There is a faint irrationality behind it, just because there was a clamour for mass testing. Hancock's 100,000 target was a response to criticism in the media, and he decided to crank out tests regardless.