Hi Id-ot ~ thanks for the extra info.

As the barking/growling has started fairly recently, has there been a particular event that you can pinpoint that started them off?

What were they like with other dogs they met off lead?

As you say, they are timid & nervous, so the growling & barking is probably more defensive aggression as in "let's get in first & scare the other dog so it knows not to come near us"!! Dogs that are nervous & unconfident around other dogs would usually choose to avoid other dogs, and they show the appropriate body language with lack of eye contact, lip-licking, the way they stand etc. Other dogs will interpret this as "I can see you don't want to be sociable" so most dogs that are well-socialised themselves & good at reading other dog's body language will leave them alone.

Unfortunately, despite our best intentions, when a dog is on a tight lead, it distorts their body language, they can't give out the correct signals to other dogs & so they are misinterpreted. Plus when a dog is on a lead, the option of avoiding another dog is taken away from them (i.e. the "flight" option) so they are left with no alternative but the "fight" option. Your dogs have resorted to this last method, i.e. let's shout at other dogs to keep them away!

Another factor is that both your dogs are unneutered males, probably in their prime of life, so it's likely that they will be attracting the attention of other entire male dogs (& some neutered ones too).

I would think that the best way to overcome these problems, is to find a calm, possibly elderly, neutered female dog to start some socialising for your dogs. If they can get used to being around other dogs off lead, in safe controlled situations, they are more likely to be less worried in other circumstances.

It is also possible that being 2 dogs always together, that they wind each other up ~ one starts barking & the other joins in. It might help to give each dog some time with other dogs on their own, without the back up of the other dog.

When introducing 2 dogs that are on lead, I always recommend that the lead remains loose so that body language isn't distorted, & the dogs feel free to interact as they want, with the option to move away if they want.

Thanks for that.
I will try to take them out seperately, see how that goes.