Whilst I generally agree with a lot of what has been said above there are one of two areas which need comment!
1). No one has said that it is cold and damp in the evenings early to mid-October onwards and you need to wrap up - we light a fire most evenings when we are over there that time of year.
2). The sea CAN be warm but that is subjective! Last year we were out 15th October and the sea water was most definitely NOT warm! The year before it was passable at best!
3). Many places start to close down the end of September and if coming out 22 October for the half term, there won't be much left open. In some smaller resorts there will be nothing open at all and nothing in the supermarkets which are open, depending where you are.
However it can still be 25 degrees during the day on a good day and it is a great time of year for walking etc.