My dog had her first season at 8 months old and for about a month before showed some out of the ordinary behaviour such as several attempts of escaping, barking a lot, full of energy (even more than usual etc). Six months on I think she's due for another season as her behaviour has changed a lot in the past week, shes barking and scratching to get out almost constantly, this morning ripped off a fence panel and tried to escape into next doors garden, doesn't settle easily and paces back and fourth etc and is gernerally driving me up the wall! As with last time nothing in her usual diet, excercise and routine. Is this behaviour usual before a bitch comes into season?

I wouldn't say usual, but to degree yes, some bithces get a little tetchy, hyperactive, snappy, clingy before, and during a season.  Her behaviour seems to indicate that her coming season is to blame.  Some bitches may try to escape usually during their peak time of season but I guess that your girl is driven to do it before.  They all react differently and many don't have any reactions at all.

If her season comes in in the next week or so, you will know for sure that it is to blame for her eratic behaviour. If not take her along to your vet for a check up, just to make sure she has nothing else going on with her.

If you are not intending to breed or show her, personally I would have her spayed approx 12 weeks after this next season for future health reasons and also to stop her hormones driving her crazy. :-)