Alan was a friendly colleague who loved being outside and talking to anyone. As a child, he developed the skill of always finding something of common interest to discuss with anyone he met, and he carried this through into his adult life. Alan was able to strike up a conversation about anything with anyone. Alan learned to scuba dive in 1970 when he joined the Leicester Underwater Exploration Club. Two years later, he became a commercial diver—a high-risk career in the early '70s—with his "office" primarily being the North Sea exploration rigs.

He was awarded the MBE medal by fellow scuba diver, HRH Prince Charles in recognition of his award-winning underwater photography. Mustard later remarked on social media that HRH Prince Charles had told him to keep taking pictures of plastic in the ocean so we can beat the problem.