After what seemed like a never ending Summer, I think we can safely say that Winter has arrived.
So, until 15 March 2015 wet (or dry) suits are now compulsory, meaning that you will not be able to participate without one, and after that it will be at the discretion of the DO until things start to warm up again.
Wetsuits should be full length 5mm suits (one described as “5/4” or “5/4/3” is fine) and dry suits appropriate to the season.