Marriage breakdown within 2 year probationary period

When does the status of the person who came to the UK on a marriage visa change if the marriage breaks down within the 2 year pobationary period? is it

A) When the marriage breaks down
B) When the Border Agency is notified
C) When the Border Agency has got round to reviewing it after being notified
D) After the 2 year probationary period

What would the status become and is the person therefore allowed to work, taking into account they are working without documents which surely must be illegal. I'm trying to get the Border Agency to do its' job but they'r not very proactive at all nor do they respond!

And also does anyone know what the UK Border Agency would do next in taking action? thank you.