Boris Johnson’s Government has over-promised and under-delivered as it proved incapable of combating Covid-19, a former head of the civil service is set to say.

In a withering assessment of the Government’s actions, Lord O’Donnell – who served as cabinet secretary to Tony Blair, Gordon Brown and David Cameron – criticises the lack of a “clear strategy” or “strong leadership”.

Lord O’Donnell, a crossbench peer, will use a lecture to argue that the Government has failed on a number of levels – it did not collect and use adequate data and deferred too much to medical science at the expense of behavioural and economic experts.

He says: “We have to ask why a country with such reputed health and intelligence institutions has been so incapable of combating the Covid-19 pandemic.

“In 2019, we were ranked second in the world for pandemic preparedness by the Global Health Security Index.

“A litany of new rules and a steady stream of leaks reflects a government struggling to emerge from firefighting mode.

“Without a clear strategy, strong leadership and the use of good evidence from a range of human sciences, there is a risk that our efforts to emerge from this pandemic will be protracted and extremely costly.”

In the lecture on Thursday for the Institute for Fiscal Studies economic think tank, Lord O’Donnell will argue that the Government “lacked – and it still lacks – a policy framework that can properly assess the costs and benefits of different measures”, partly because medics have informed the strategy more than other branches of science.

He will claim there have been “political attempts” to blame Public Health England for the difficulties encountered in tackling the virus but suggested that ministers must also take responsibility.

“At this stage, we cannot reach firm conclusions about which parts of the government machine are responsible for the various operational failures in areas like testing and the supply of personal protective equipment (PPE),” he will say.

“On the testing side, it is hard to understand why PHE rejected the use of non-government laboratories. Other countries, like South Korea and Germany, successfully used a much more decentralised approach to testing.

“In addition to some operational failings, ministers have frequently broken one of the cardinal rules: they have over-promised and under-delivered.

“Talk of moonshots shows they have not learnt this lesson yet.

“That puts enormous pressure on the system and results in behaviours which ‘hit the target but miss the point’, like sending out lots of home tests which are not returned.”

He claims the Prime Minister “used up his political capital” soon after leaving hospital following his treatment for coronavirus – largely by supporting his senior aide Dominic Cummings following his apparent breach of lockdown rules.

“The Cummings debacle is where much of that capital was expended, and alongside other failings points to something we knew already: optics matter,” Lord O’Donnell says.

Ahead of the lecture, IFS director Paul Johnson said: “As Lord O’Donnell makes clear an effective response to this crisis requires the best use of all the available data and evidence, including from the social sciences.

“Throughout, the IFS has been compiling such evidence to demonstrate the impact of Covid and government policy on the economy, on inequalities, on mental health and wellbeing, on education, and more besides.

“It is crucial that government weighs up all this evidence when determining its policies. If they are led by the medical science alone we won’t follow the best path out of this crisis.”