Hi Foxmoth,
Can't remember the exact wording and don't have the book to hand but the law basically states you can break any of the rules if you need to in order to be safe.
Yes, the ANO does provide this lifesaver, but if you have need to break the rules, the CAA must be informed at the earliest opportunity (or words to that effect). I don't imagine the CAA will very relaxed about it.
DFC,
The ANO requires a pilot not to depart unless the flight can be completed as planned......if you plan a VFR flight then you can not legally depart unless you are (as much as possible) sure that the flight can be completed VFR.
The only reference for the requirement of uninterupted VFR is in relation to cancelling IFR flight plans in controlled airspace or license restrictions.