I have to cavlier king charles spaniels both 3 one we have had since a pup(henry)( the one we are now but only recently having a problem with) is loverly with some dogs and will play happly and is very affectionate towards some people but ceartain people or dogs he will bite and i am struggling to find a reson for this.
The other one is a female but has being done (sophie) we have had her just over a year now and when we had her she was very over weight and scared and wary of all dogs and petrefied of men. She has over come her fear of men and now has no problem with them but is still scared of some dogs but has gained confidence .
Does henry try to protect her and how can we stop him.

First of all can I ask if Henry only does this when he is with Sophie or if you walk him on his own does he still act this way.  If this only happens when he is with Sophie I would assume he is protecting her and that maybe you need to work on her fear.

Obviously if henry does this even when he is on his own then you need to work out what triggers him and therefore how to build his confidence in such situations - maybe a bit more information about how and when this happens and we may be able to give some more advice

good luck

Have you had his eyes tested?  One of my girls is partially sighted as her lenses never developed at birth.  She is not nervous but doesn't like people coming up to her and touching and takes a while to get used to dogs and people that she doesn't know.

We never realised until she had her general eye test that there was anything wrong, although did wonder how a dog that looked extremely confident when she walked into a room wouldn't allow everyone to touch her.  Now I tell people not to bend over her and touch her.  If people listen to me she is all over them after about 20 minutes as she has gone up to them not the other way around.