B1rdonawire "...whining is, IMO, a bit like a baby grizzling to sort of let you know they're still there and they need something from you. It's very effective, in that it does get your attention..."
I had not through of it like that. I will try and think of it in that way.
Sadly, IMHO it is not really effective. It just ends up inflaming family situations and causing more stress. I've tried to work out how to help him. We had a year of Theraplay and this has really cut the 'temper tantrums' (for want of a better word) by about a half, it has been really good and has really helped him.
Sadly, the moaning continues. Even after a really nice day when we have done whatever he wanted to do he still finds something to complain about!
"When you can in our case after the event try to see the attention-seeking behaviour as in fact attachment-seeking behaviour? I find it takes the irritation out of it for me" Can you tell me more about this, please? How you do it? 
OK, will look for books by Margot Sunderland, and Sarah Naish. ("Willy and the Wobbly House" and "Teenie Weenie in a too big world" - I like the idea of opening up chats about worries lurking underneath other behaviour.
"I don't know how much your DS would be able to process whether or not his friends' families are put off by "moaning", and I'd be very wary of triggering feelings of shame in him, so I wouldn't mention it."
Too late, I am afraid I did mention it, but I won't next time. He is quite a confident little boy usually, and generally acts like he is very sure of himself but I will try and see the moaning in relation to this and see it as lack of assurance in him.
Crisp well done on coping so well when your dd started talking about her past.
We have tried with ds to talk about his birth family, well I have, but he is very reluctant to do so. And even being reminded it was the anniversary of the time he came to live with us seemed a bit distressing to him so we dropped it. I think I will just need to wait until he starts talking about it. Maybe these books will help him find the words or the thoughts to think about it.
I feel so shit now for not realising all this. We've done loads of theraputic parenting things over the years but this moanyness is so like 'regular moaning' which we get from our other child, and after a while it is incredibly draining. 
I love the idea of your bedtime chats and sofa chats, we have done this and still do but not enough. DS is quite reluctant to do any kind of serious talking, it is always 'funny voices' (me) and tickles (me) and that kind of stuff. But I will make more effort to be in the right place and hope it will be at the right time.
Ironically, as he has got more confident and self assured he has got less affectionate and seems to need me less! It can feel like a mine field.
Crisp "After a while I'd just say "tight knickers?" when she was whining and we'd make a joke of it." I am going to copy this, except it will be tight pants.
"Don't know if any of that helps." It does, it is immensly helpful, thank you all.
Crisp love the idea of "whispered ... code word" Will use that too.
PoppyStellar thank you I was feeling quite a shit mum and I read "you are not alone", thank you.