Jonathan is the founder and president of what is now Prostate Cancer UK. In 1996, he established The Prostate Cancer Charity, the first United Kingdom national organisation promoting research and patient support for prostate cancer.
The organisation has since merged with Prostate Action, becoming Prostate Cancer UK, the biggest organisation of its kind in the UK. The charity lobbies for change for prostate cancer patients, funds research and provides a national and regional patient support and information service. In 2021, the charity funded a study investigating why black men are twice as likely as other men to develop prostate cancer.
Jonathan has been the Flow Foundation Professor of Oncology at Imperial College London since 2011. He established a clinical and laboratory research programme there, leading a laboratory research team tasked with understanding the mechanisms underlying the growth of prostate cancer. He continued to carry out clinical duties.
Jonathan helped establish the All-party Parliamentary Group on Cancer, the organisation behind the Britain Against Cancer movement.
He has published around 400 research papers and book chapters, and 16 books on cancer. He has also written a medical law book, a novel and a book of short stories entitled The Elephant in the Room, published in October 2011.