connecting 2 extractor fans on one plug

That doesn't sound Regs. compliant. If you have a hot tub inside a room I would interpret that as a room containing a bath. This comes under Section 701 of the Wiring Regulations. You should not have any sockets in that room at all, not even weatherproof ones. Its classed as a high risk area and sockets are not allowed. You may be able to use spurs if you need ventilation but I can't advise any further without the benefit of seeing what you have built. You would be strongly advised to remove the sockets. Edit: Yes, if you move the sockets outside the room you can use them. If I am not mistaken, the hot tub would come supplied with an inline 10mA RCD. You must not remove it, its there for your safety. So pushing the flex through a wall to a socket would require temporarily removing it. I don't think 16A (Commando?) sockets are appropriate here you would use standard 13A sockets. A better and safer solution is to use 13A switched spurs. You would hard wire these. No plugs needed, you would cut them off.