We got married in November. An outdoor summer wedding was not something we HAD to have and in the end we like the idea of a cosy indoor reception with lots of candles and an open fire. We just assumed the weather would be bad and made sure that the venue was lovely enough inside to accommdoate everythign we wanted, had umbrellas on stand by etc. In the end the weather was ok for the most part, we got a few outdoor photos at the church, but then it started raining so we had more at the reception indoors rather than out. They are still lovely tho.
We did move the ceremony slightly earlier than we had originally planned on the advice of the photographer to maximise the amount of daylight, ceremony was 1.30 instead of 2 we had originally considered.
We felt at least in winter you can plan for the worst weather and not be dissappointed, just a bonus if you get sun. Whereas in the summer you will always hope you are going to get a beautiful day and you can never rely on in it here. Plus it meant we got several out of season offers eg from venue, photographer, car hire and so saved a bit mof money (although I wouldn't say it was loads).