Boris Johnson has pulled out of a committee meeting in front of senior MPs on less than a day's notice, saying he needed to "focus on delivering Brexit".
The prime minister was scheduled to appear before the Commons Liaison Committee - made up of select committee chairmen - in Westminster on Thursday.
But with less than 24 hours notice, Mr Johnson asked in a handwritten note for a new date to be arranged for "five or six months" on from when he became prime minister.
In her reply, Dr Wollaston said his refusal to be held to account – having cancelled two previous appearances – was “unacceptable”.
In his note, released by the committee, Mr Johnson said: “I promised that I will come to the Liaison Committee and I will keep that promise but I am afraid I must now focus on delivering Brexit in the difficult circumstances in which we now find ourselves.”
He said that delaying his first appearance until five or six months after he became Prime Minister in July would be roughly in line with what happened with his predecessors Theresa May, David Cameron and Gordon Brown.
In her reply Dr Wollaston said: “Frankly, I am astonished that, at such short notice, you are refusing to face detailed scrutiny from select committee chairs tomorrow morning.
“It is unacceptable that you are refusing to be held to account.”
The committee hearings – which normally take place three times a year – are an opportunity for members to put detailed questions to the Prime Minister on selected policy areas.
Mr Johnson had been due to be questioned on climate change and health and social care policy as well as Brexit.