You're right about Maxwell. The other two have already appeared on banknotes. (The ones highlighted in grey have already appeared on banknotes, though there's

You're right about Maxwell. The other two have already appeared on banknotes. (The ones highlighted in grey have already appeared on banknotes, though there's some inconsistency between the highlighting and Wikipedia's list of people on UK currency.) Other scientists, mathematicians, and technical innovators already honored: Kelvin, Darwin, James Watt, Florence Nightingale, George Stephenson, Alexander Graham Bell, and Alexander Fleming.