Mr Keech has died at the age of 90, said Keech Hospice Care – the Luton charity he helped fund.
In 1997, with his wife Shirley, he donated £1m to begin the charity’s appeal to build the hospice.
At the time of the appeal, he said: “I’m thrilled the children’s hospice has reached this stage so quickly. I just wish it wasn’t necessary in the first place.”
It opened in 2000, when it was known as Keech Cottage.
Ms Searle said: “Mr Keech was a remarkable man, a very clever businessman and a passionate supporter of Keech Hospice Care.
“We met regularly and he always had advice and ideas.
“He will be very much missed by all the staff and volunteers here at the hospice – irreplaceable.
“Our thoughts are with his family and friends at this sad time.”
She added that he was widely known for saving the Dunstable wiper business AC Delco from closure and he had links to the manufacturing, property, telecommunications and design sectors.
In 1996, he was appointed Officer of the Order of the British Empire (OBE) for services to the motor manufacturing industry.
“Without Dennis’ incredible generosity and continued support, Keech Hospice Care, as a charity, would not today be able to care for seriously ill children or support their families, making the difference when it matters the most,” said the hospice in a statement.
“Our children’s service is Dennis’ legacy and he has left the community a remarkable gift.”