Unless you want to run the risk of an electric shock.
You must plug the cable into the caravan first and then plug into the hookup post. If you have access to the isolator for your EHU on the post, switch it off. Then when connected, switch it on. That way you avoid risk of electricution.
These days with hookups very near the pitch, a 25Mtr cable is often 3 times longer than needed and people leave it rolled which is wrong. A coiled/rolled cable generates excess heat which can break down the insulation of the cable, causing a short circuit. So first off unroll your cable fully. Better still. I would cut it and fit another plug and socket giving you a 10Mtr cable and a 15Mtr cable. This fit's most usages. My 15Mtr cable fits nicely to our van from the EHU and lies flat to the ground.
My bro-in-law used a 50Mtr 240v extension lead only extended 5Mtrs to run a 3KVa 110v transformer to run tek guns on a building site. After half an hour the power went off. He found he had got a moulten roll of extension cable costing him £40 to replace. I've also seen the same "chuckle brother" put a 6mm hex drive bit into the 13 amp plug instead of a fuse rather than findout why the fuse was blowing!
Frightening isn't it, how some folks don't know how to treat the silent killer called electricity
Even a damp cable is enough to transmit electricity so simply isolate before plugging in or out and do it at the post.