UK Auto Repair Questions?
The fans are controlled by the temperature gauge sender unit on top of the water pump via the engine ECU
so for them to suddenly come on either there's a wiring issue on the relay socket , or a faulty relay or a faulty sensor
most likely is the fan relay itself is switching when it shouldn't so I'd say to pull it out and fit a new one as they are only a few pounds
the relay should be in the engine bay fusebox and marked up on the lid as to what relay is what