Is there anything to stop me putting Bettas in with My goldfish?

Other then the fact that your already over stocked... yes. I guess the main reason is bettas are tropical and goldfish are cold water. But I'm sure someone else will come along and tell you more reasons

We may be getting a tub, thats all.

goldfish will pick at the tail of the betta, but as you are going to get somewhere else for it to go then all is good.
how many gallons is your tank with the goldies?

The goldfish may become more agressive and attack the bettas. Or vice-versa. also, bettas need diffrent water conditions than goldies (i think) I wouldnt risk it. BUT since your getting a tub I think you could put a betta in your old 16ltr tank. Im sure they would be very happy there hope this helped!

Thanx
Only problem is mum and persuading her that there is space for the tub. Somewhere......

Hun I hate to be a bubble burster, but I don't think you should plan to get anymore fish at the moment untill you actualy have an extra tank. Someone already stated that you're over stocked, and you said yourself you're not sure your mom will let you get anymore. It's better not to continue getting more and running out of room, that only puts the fish in unfavorable conditions. It's a good idea to wait on the thought untill mom gives you permission, nothing against you, I'm sure you'd rather have nice tanks with happier healthier fish than overstocked ones. Just something to think about. Good luck for the new tub, maybe try for a pond, tubs usualy turn into tubs anyway.

When I first started out with goldies, I had my betta in there and after a few days the betta was chasing one of the goldies and nipping the fins. I would (and do!) keep them seperate. Maybe if you get a tub for your goldies, the betta can have the tank they're in now.

I find this kinda funny, because a while ago, when I got one of my bettas, a petstore was acctually putting their bettas in with the goldfish tanks. I was shocked. They claimed they were doing fine, but from what I saw, the bettas were chasing all of the goldies around, and really stressing them out. I really wouldnt advice putting them in together. They really arent compatable. I hope you can get a new tank, just make sure your prepared for the extra work.

Good Luck

both of the fish will fight with each other. betta like warm, gf like cold water.