Welch's mother died when he was five and he was raised by his aunt.
In 1957 while still at school he formed a band called the Railroaders. After winning a talent contest in London the following year, they were asked to join Cliff Richard's backing band, The Drifters, which later became The Shadows. He was more than just a band member; he produced albums for Richard in the 70s, wrote some of Richard's best-known songs and "discovered" Olivia Newton-John. He stayed with the band for the next 30 years, with only one short break.