Just wanted to announce to all a bit of good new re: this thread
Bit of a 'HA!' moment, really.
The mate of mine's ex missus, who was threatening him and using the kids as a bargaining chip etc... has split with her super-duper new feller. She has now suddenly started to be reasonable again, offering to go out for a McDondalds etc.. to have a talk, money she owed him she has started to pay back, she's said he can see the kids any time he wants, told him he
is a good dad. He had the kids stay over at his all weekend (he's not even
seen them for about a month

)
No-one can say what'll happen tomorrow, or what some other 'new bloke' will whisper into her clearly impressionable ear, so perhaps a little premature to call this a 'happy ending' - however, this is, at the very least a good outcome.
I personally want to say thank you from myself and him for all your advice. I printed off all your responses, and I'm sure it helped. He kept his cool, didn't let emotions get the better of him, and he's been pretty much 'whiter than white' through the saga, and she's had no ammunition to use against him as a result.
Thank you again. 