if I am right the 100 started in 1987 not long after the Metrocentre opened. But there was also a 101 and 102 if I remember correctly. The 101/2 possibly 103 and 104 also got changed to at least the 54 and were operated by Blue Bus/Armstrong Galley and operated to the outskirts of Heddon on the Wall etc. So the 100 was part of the original batch of Metrocentee 1xx services