(Yesterday, 4:47 pm)F114TML wrote Broadly I believe,
1-99 Newcastle & Gateshead
100-199 Wearside
200 - 299 East Durham
300 - 399 North Tyneside
400 - 499 Washington (I think)
500 - 599 South Tyneside
600 - 699 Hexham, etc.
700 - 799 West Durham/Derwentside
800 - 899 Not sure
900 - 999 special/workers

Anyone able to add/ammend?

800 - 899 were independent operators eg. Hunters 
There was also a few exceptions like the long distance services to North Northumberland which had 500 numbers and Jolly in Sunderland which never had a route number whilst independent. The 294 ect. services only came after de-regulation.