You should bring a wetsuit to every event. Under British Triathlon rules wetsuits are either mandatory, optional or forbidden depending on the combination of swim distance and water temperature.
Up to 1500m: Forbidden above 22°C (24.6°C for Age 60+), Optional between 22°C and 14°C, Mandatory below 14°C
1501m+: Forbidden above 24.6°C, Optional between 22°C and 16°C, Mandatory below 16°C
Mandatory wetsuits must cover at least the torso.
You can wear any type of wetsuit including shorties.
Where wetsuits are mandatory, socks are permitted. Gloves are not permitted.