A charity is to receive up to £50m following the deaths of publisher Miles Blackwell and his wife, Briony.

Mr Blackwell was the retired chairman of Blackwell Ltd, the Oxford publishing and bookselling firm.

He died in August, aged 56, of an internal haemorrhage, three weeks after the sudden death of his wife, Briony, 45. She had had a long battle against a rare disease, multiple chemical sensitivity, for which there is no known cure.

They had no children.

The combined estates of the couple, amounting to £30m, have been left to the Tubney Charitable Trust, a grant-making charity created by Mr Blackwell in 1997. It is also thought the charity will receive a further £20m from the Blackwell Family Trust.

Jonathan Burchfield, one of the executors of the wills and a trustee of the charity, said: "It is a wonderful gesture from Miles and Briony. It is a massive task for the trustees but it is also a wonderful opportunity to do huge amounts of good and worthwhile work."

The trustees intend to make grants to charities undertaking activities in environment, animal welfare, education and medical research.

Mr Burchfield said: "We are trying to concentrate on areas that would comply with the wishes of Miles and Briony."

Mr Blackwell joined the Oxford publishing and bookselling firm in July 1966, becoming the third generation of the family to work there at the same time.

In the four years before his death, the charity gave about £100,000. Donations granted in Oxfordshire by the charity, since it was established five years ago, have included funding the purchase of three new windows in the chapel of New College, Oxford.

The Blue Cross Animal Sanctuary, based in Burford, has also received funds from the charity.

The estates are being dealt with by White & Bowker of Winchester, Hampshire, and the charity is being administered by the Charity Group of Nabarro Nathanson.

Details of grants available and the application process are available on the website www.tubney.org.uk or by writing to Catherine Small, Nabarro Nathanson, The Anchorge, 34 Bridge Street, Reading RG1 2LU.