So what is 'unreasonable behaviour'?
There is no such thing as no fault divorce. This is because the 1973 Act of Parliament (now 44 years old and many say painfully out of date) sets out the grounds for divorce and provides a limited framework for a divorce petition to be acceptable to the court and for the parties to ultimately divorce. There are other grounds for divorce, but very often these are not available to the parties. It is for this reason that a divorce based upon 'unreasonable behaviour' is so very often the only way forward.