Someone might know the Answer: My Difficult Easter Quiz a real Gem

I could have just posted this amazing find for whilst going through my old PSV News Sheets typing out individual garage allocations i stumbled upon something worthy of Qi so I thought we could have a little fun with it.The remarkable thing is I had found a depot which housed seventeen buses and every single one had the number nine in it, indeed there were twenty-six number nine digits in the registration number but two lots of three buses were in sequence.I know buses moved from depot to depot so it might have not stayed like this for long but the chance of number nine appearing on all seventeen bus registrations is like getting all the no score draws on the football coupon stumbling into millions of quid. This one will no doubt only appeal to the older bus anoraks among us as the date was May 1967 and your only clue is it was one of the BTC/Tilling Group. I will post up the answer to my little mystery on Easter Sunday so lets see if anyone else knows which company and garage it was.