Mitton wrote six episodes of "TUGS" and directed nine of them. When Clearwater Features closed down, he joined the Britt Allcroft Company.
Although some episodes were based on Railway Series books, some of the script was written by him and Britt Allcroft. After the death of the Reverend W. Awdry in 1997, Mitton and Allcroft decided to create stories of their own. His last episode as writer was Edward the Very Useful Engine, but he continued as director until Three Cheers for Thomas before retiring. Steve Asquith replaced him as director from then on. David was also a model unit creative consultant for Thomas and the Magic Railroad.
He was working with Gerry Anderson producer David Lane with their own company "Pineapple Squared Entertainment", which was due to launch a new CGI Animation series "Adventures On Orsum Island". Only a few episodes of "Orsum" were semi-completed before his death.
Sadly, David Mitton suffered a heart attack and died on May the 16th, 2008, at the age of 69. His death was not announced until May the 28th, 2008. Many "Thomas the Tank Engine" and "TUGS" fans were greatly saddened by this news.