The ex London one's you speak of were these things I always remember them being left in the Arriva London livery for a while with Arriva Serving Northumbria logos on them and a green ball where the red one would be for London. They were wasp hives towards the end though.

https://flic.kr/p/icQiYd

https://flic.kr/p/icQJkM

https://flic.kr/p/icQJPT

The BYD Decker's I saw one on test a few weeks back driver familiarization I think it has engineers on also it was on Village Road, High Pit Cramlington. Since then I've not seen anymore though I am surprised they didn't come in the Eco livery.