Okay so I am low on that grey gummy sealing tape for vacuum bagging, is there anything else that's just as good. Can wide sellotape be used to seal the ends of a vacuum bag if the mould was going directly inside of it? 

I would say no. It might be, that someone has successfully created a leak free bag once or twice, but it is definitely not a reliable method. Tacky tape isn't that expensive. A single failed attempt will cost you that much more that it is 100% worth it's money.