The board of the UK asthma inhaler maker Vectura has unanimously recommended that shareholders accept a controversial GBP1.1bn takeover bid from the tobacco company Philip Morris International, despite warnings from health charities and public health experts.

The Vectura board said it considered the terms of the final PMI offer “fair and reasonable”. They added that “wider stakeholders could benefit from PMI’s significant financial resources and its intentions to increase research and development investment and to operate Vectura as an autonomous business unit that will form the backbone of its inhaled therapeutics business”.

The move came despite more than 20 health charities, public health experts and doctors sending a letter to the board urging them to reject the bid.

PMI had raised its bid for Vectura to 165p a share last weekend, valuing the firm at GBP1.1bn and outbidding a rival GBP958m offer by the US private equity group Carlyle, which had agreed a takeover of Vectura in late May.

Sarah Woolnough, chief executive of Asthma UK and the British Lung Foundation, said the charities were “extremely shocked and concerned” at the news. “PMI makes billions every year from making addictive products that can cause and exacerbate lung diseases. It’s totally absurd that PMI could make more money from providing treatments to the very people they have made ill in the first place.

“We will continue to oppose this dreadful proposed takeover until a final decision is made. We appeal now to Vectura’s shareholders to make the right and ethical choice and say no to big tobacco.”

The letter to the board, signed by heads of charities including the British Lung Foundation, Action on Smoking and Health (ASH) and the American Lung Association said: “Vectura’s future commercial viability as a company dedicated to improving respiratory health would be seriously jeopardised should the PMI takeover proceed.”

It noted that Vectura generates the bulk of its annual GBP200m revenues from making pharmaceuticals that treat smoking-related diseases such as chronic obstructive pulmonary disease. It suggests that if the bid by the Marlboro and Chesterfield maker is successful, PMI would “profit from treating the very illnesses that its products cause”.

The letter also said that “2020 was the worst year on record for the negative impact of tobacco on human health, causing an estimated 8m deaths and tens of millions of serious medical illnesses. PMI has an estimated 15% share of the global cigarette market, yet it is not held accountable for the profound impact its products have on human life”.

PMI says it advocates a smoke-free future, but still makes about three-quarters of its $28bn (GBP20bn) in annual revenue from “combustible” products that involve the burning of tobacco.

Carlyle said on Tuesday that it would not raise its 155p a share offer, which valued Vectura at GBP958m, describing it as “full and fair”. The private equity firm also insisted it would be a better steward for the company, its employees and patients than PMI. Vectura shares are trading at 163.2p.

Speaking before the announcement, the shadow health secretary, Jonathan Ashworth, said PMI’s bid “beggars belief” and urged the government to “stand up to this tobacco giant and block this takeover”.

Nicholas Hopkinson, the chairman of ASH, said the idea that PMI could “schmooze its way into healthcare, or in any way launder its reputation, is morally repellent”.

“There are several ways in which a PMI takeover would damage Vectura,” he said. “Firstly, loss of scientists who will not want to work for the tobacco industry; secondly, loss of ability to collaborate academically or perform clinical research; thirdly, loss of income stream as doctors are unwilling to prescribe and patients are unwilling to use inhaler devices that would be providing royalties to the tobacco industry.”

Vectura was founded by academics at the University of Bath almost 20 years ago and specialises in developing respiratory drugs. The firm is working with another UK firm, Inspira Pharmaceuticals, to develop an inhaled formulation of the latter’s plant-based leading drug candidate for the treatment of Covid-19.