Lord Kerslake has resigned as boss of King's College Hospital because of funding problems with the NHS.
The House of Lords peer announced he was stepping down as chairman of King's College Hospital NHS Foundation Trust in London on Sunday.
He said in a statement: "I do not do this lightly as I love King's but believe the Government and regulator are unrealistic about the scale of the challenge facing the NHS and the Trust.
"I want to pay tribute to the staff and their excellent patient care."
Lord Kerslake paid tribute to the "world-class" care given at the hospital, especially after the Westminster and London Bridge terror attacks, in a self-penned Guardian article.
"King's, like many other hospitals, is fighting against the inexorable pressures of rising demand, increasing costs of drugs and other medical supplies, and the tightest spending figures in recent times," he wrote.
He added: "There are undoubtedly things that I and the trust could have done better, there always are, but fundamentally our problems lie in the way that the NHS is funded and organised.
"We desperately need a fundamental rethink.
"Until then we are simply 'kicking the can down the road'."
The hospital described Lord Kerslake as a "passionate advocate and champion" of the trust.
"With a heartfelt commitment to staff and patients, he has led King's through a challenging period which has also seen some notable successes, our response to three major incidents in London, the launch of the helipad and delivering some of the highest patient outcomes of any Trust in the UK," a statement added.
"We would like to express our deepest thanks to Lord Kerslake for his hard work and dedication not only to this trust but to the core values of the NHS, putting patients first."
Lord Kerslake is a member of the House of Lords, president of the Local Government Association and former head of the civil service and permanent secretary at the Department for Communities and Local Government.