The 51-year-old jumped from the Langstone Bridge to help a man who was being dragged out into the harbour by the currents.
The drama came as PC Skinner was on his evening shift and was the closest officer to the scene when a member of the public reported seeing a man perched on the railings.
PC Skinner arrived at the bridge at about 9.35pm and called the coastguard, RNLI and other emergency services before starting to chat to the man, who by this point had climbed over the barriers and was gripping on to a lamp post with one arm.
PC Skinner, who serves with Hampshire Constabulary’s dog unit and lives near Emsworth, said: ‘I spoke to him and he told me he had had enough and was going to jump.
‘The tide was reasonably high and there was quite a flow of water under the bridge.
‘I continued chatting to him and it turned out he had served in the army in Northern Ireland and was suffering from post-traumatic stress disorder.
‘I had served in the army and in Northern Ireland for two years and it rang a few bells with me.
‘We could have swapped positions and been on opposite sides but for events that have happened in our lives.
‘I told him that if he jumped, I was going to jump in after him.
‘He said he didn’t want me to jump in, but I said it wasn’t negotiable because that was my job.
‘As a police officer you are expected to save life and limb.’
The man lost his balance and found himself hanging with one arm over the fast-flowing water.
PC Skinner said: ‘I climbed over the barrier to grab hold of him and with that he let go and dropped into the water.
‘By then I had no option. I jumped in. By the time I hit the water and re-surfaced I was under the bridge because of the tide.
‘I remember when I hit the water thinking “this is not a good idea because this is cold”.
‘It was freezing cold.
‘The man was a good 10 or 15ft away from me and the tide was taking him out.
‘I remember shouting at the other police officer as best I could “throw the life ring”.
‘I swam out to the chap and grabbed hold of him and swam back to the life ring. By then red mist had taken over and I didn’t want to be messing around.’
Other police officers dragged the pair across to the shallows where they were treated by paramedics and put in thermal suits to keep them warm.
A Hayling RNLI lifeboat arrived at the scene, but by that point the pair were already ashore on the slipway to Langstone Sailing Club.
The man, from Waterlooville, was taken to Queen Alexandra Hospital by ambulance for treatment.
The incident happened on December 27.
PC Skinner, who has been in the force for 15 years, added: ‘It was very cold and an experience I wouldn’t want to repeat in a long time.
‘I became very determined and focussed that I hadn’t jumped in the water to die myself.
‘I don’t feel like a hero. I’m sure every police officer in my situation would have done the same.’