I met David, almost 10 years ago. He was an incredibly energetic and driven man. I worked with him on and off over the last decade, and although he and I had different views on the world, I respected him greatly.

He so wanted to help develop our new treatment methods to ensure that more and more people benefited from them. He literally cajoled me into a meeting last year with Cancer Research UK where we argued for, and won, special treatment from them for our work.

 David did not let us academics off lightly. He was tough and forthright. If he felt we were pulling our weight to raise public awareness and do the right clinical trials, he would tell us. And if we were not, he would tell us that too.

In fact, he really helped us concentrate on what was important, to ensure that we bring new and potentially beneficial cancer treatments to the right people as quickly as possible. In an area of medicine where progress takes decades, he challenged us to turn the pipeline into years. He made us sit up and think and at the same time, he successfully engaged influential people in the public arena to support our work.

 David was unique. He will be missed by so many. It is very sad that he will not be around to see the fruits of his own labours as they mature over the coming years. The world is a poorer place now that he has left us..

- Professor Laurence Lovat BSc PhD FRCP

David Longman was a roller coaster to work with across the years before he dedicated his life to the PDT treatment for his daughter. He was sometimes a great joy, sometimes a real challenge - but first and foremost he thought nothing was impossible. He achieved some amazing and apparently impossible things.

He gave 200% and expected the same from whoever he dealt with. That meant that he got upset with anyone who didn't automatically see that David's hugely ambitious idea was achievable - so he fell out with people as frequently as he impressed them!

I worked well with David - he broke down closed doors and I came in and politely put them back on their hinges. I shall miss David - a gentle giant who was a great and loyal friend.

- Douglas McArthur, PLANNING FOR RESULTS

Dear David, I'm deeply saddened to realise you have passed away. You so kindly called me at home to offer your support and guidance and friendly ear. Your humour, strength of character and pioneering work will never be forgotten.

David truly did make the world a better place, he kicked open shut doors...he saved lives with his passion for his work. my sincere condolences for your family and friends. I'll miss you David, I'm proud to call myself your friend, I just hope you knew how appreciated you were.

RIP David - your kindness, generosity and strength of spirit was so apparent even in the short time we spent with you. My heart goes out to your family and friends. The world needs more human beings like you. Thank you for all your hard work helping others xxx

Not long ago we met an incredible man. Very rarely do you meet someone so inspirational, so supportive and so willing to go the extra mile for you, or in the fight against cancer. This view it seems was shared by so so many people. I don't know how many lives were helped and even saved by this very special person, but the world needs more people like him.

Rest in peace David

- From patients & friends

I'll miss you David. Who else would be so excited that they discovered you could add raspberries to curry and make it sound good.

RIP I'm so sad I can't think what to write David...

Thank you for the many years of love and laughter we shared... two am curries with David Gates... singing with Kate Bush... many happy fun, silly but great times as well as your fantastic work with Killing Cancer... you helped so many and asked so little, you will be missed by all your many friends.

David, thank you for being my friend, I will miss you big man x.

- From patients & friends