Divorce pakistani wife

[Spring12]

I am a British citizen - male

I married about 6 years ago in Pakistan to a pakistani national

she came to england and stayed for 2.5 years and went back to pakistan as we were having problems

we have been separated since then and i only spoke to our children until she stopped letting me speak to them (british citizens but living with her in pakistan)

we have never formally divorced although we are now beyond reconcilliation and i want to take this step

she is now trying to blackmail me into applying for her to come to the uk as my spouse. I have refused. do i still need to inform the home office that we are not together or can i apply straight for divorce - do i need to do this through the UK or via pakistan as she is a pakistani citizen (she did not stay long enough for settlement)

Please assist.

Many thanks