I own a 7 year old whippet cross bitch who is very submissive with other dogs and used to live with my staffie cross until he died last year aged 15. I have just taken on a 3 year old collie/terrier cross and am getting concerned about some of his play.
We walked them several times before getting him and for the first week all was well and they were getting on fine although not playing together or cuddling together. Now he has started to occasionally keep jumping at her biting her ears and jumping on her back - she usually just backs away from him until she is pressed against a wall or in a corner. All the time he is doing this he is growling and she is usually staring at me rather than him which makes me feel I should be helping her. Is this normal play which will resolve itself or should I be stopping him when he does this and she backs away? At other times if she has a toy and he comes near she will growl and he then backs off so she can stand up for herself but does not when he keeps jumping at her.
They are both neutured although he has only been neutered shortly before we got him so I don't know if this has any bearing.

Your the boss, if his behaviour is unacceptable to you .. intervene and tell him NO :-)

As Leigh has said if the behaviour is unacceptable then put a stop to it.
On the other hand they could just be deciding the pecking order, I think your whippit cross will tell him when she has had enough. IMO oppinion I think he is testing the ground to see how far he can go. Try and let them sort it out between themselves but be on hand if things get a little too rough. Remember YOU should make it known that YOU are the pack leader.

Good Luck and why not join the group and keep us posted how you get on

Your whippet knows you are the boss and is actually looking to you for 'permission' to chastise the wee one. She does not necessary want you to intervene but is worried what you may do if she tells the pup off herself.

I have a beagle pup and three adult cats. The cats do the same to me. I turn away but stay very close and peep. The cat usually taps the dog on the head with no claws and this is then sorted for that instance at least. So far, in the two weeks we have had the pup we have had no serious nastyness happening.

I agree with the other comments too.

HI, I may get slated for this post but its just what I would do rightly or wrongly in this situation. Others have said quite rightly that YOU must show this new dog who is the pack leader and not leave it to the whippet. Next time he starts this behaviour I would either pick him up by the scruff of the neck or get hold of his collar saying NO BAD DOG, very firmly, and deposit him unceremoniously outside for 5 minutes, completely ignoring any pleas to come back in, til either the 5 mins is up or he's stopped asking to come back in. Once he comes back in dont hold it against him - act normally and repeat if needed. There are other things you can do to discourage dominant behaviour, like insisting YOU go through doorways first - never let him push in front of you. If he has been allowed to sit on the furniture - dont let him any more, but let the whippet if she has been used to this. Give the whippet her food first and put his bowl down second. Everything you do with/to both of them , like putting leads on, he should be second in line. Work on "Sit stay" and general obedience with him on his own with lots of praise when he gets things right.

One other point - if your bitch is naturally submissive it may well be that they resolve the pecking order between them and your new dog ends up higher up the order than her (obviously as others have said, you should be overall "top dog"). If this does happen, you should reinforce the pecking order which occurs naturally. This may go against the grain, as your bitch was there first, but it will only unsettle the dogs and prolong problems if you insist on trying to treat your bitch as the top dog after you, and the new dog as bottom of the pile. By reinforcing the natural pecking order that evolves, you will reassure your dogs and give them confidence in their relative positions.

Naturally, any aggressive behaviour or attempts by the new dog to dominate you is a different matter and should be dealt with accordingly.