Everyone, everytime-family to strangers, hes straight on his back!!!  Hes very confident and friendly,  so why does he do it?

I don't know much about gestures but it's surely a sign of trust?

He may be confident, but submissive. He is showing submission and respect to your visitors. How old is he?

hes just 4months, 18wks, its not just visitors its passersby in the street, today we met a lady in the woods-straight on his back in the mud!!!!  argh!

lol Sounds like a playful submissive puppy to me :) Good stuff :-D

I have a year old Spaniel who rushes up to people and throws himself at their feet still. At home we also have a male Border Collie 8 weeks younger than my spaniel, the spaniel is the top dog at home. I am not sure its a security issue. Whistler is fine with other dogs, has had his nose bit once! by an old old dog that wasn't having any of his tail wagging. I just think he does it to show 1) he is friendly & 2) love me. He does not show his "bits" to other dogs or his mate at home, so no submissive gestures to other (possibly more dangerous dogs) excuse me he is just up on my lap and he has been in cow pooh!!

Viv

He's just saying hello and I'm a friend here's my belly !! My terrier mix who's 4 loves everyone and does this to utter strangers.
Its a sign of being passive and friendly pup's do it to older dogs also, so to say ok your bigger than me don't beat me up.  

my one year old CKCS does this with everybody too - wherever we are...