"I've been on 'Mastermind' - I tied for first place and then lost on the number of passes. My subject..." — David Harewood

Back in 2005, the Anthony Nolan Trust could have asked me just to speak out about the lack of ethnic minority donors on the bone marrow register, but that would have meant nothing if I wasn't prepared to join up myself.

Support for charities takes many forms. Some people give their money, some their spare time. I give my name and my voice. We give what we can to make a difference to the people and issues that matter to us. But what's most important, especially for celebrities, is giving our genuine commitment.

As an ambassador for the aid agency Cafod and the Anthony Nolan Trust, I need to be sure that my public support for those charities is a help for their work, not a hindrance.

I hope my kids can experience the seasons and a climate that's sustainable. The idea that things are going to be so very different for them is slightly scary.