"He had loads of clothes on and was starting to take them off.

"His head went under and he swallowed water. I swam to a nearby boat and grabbed hold of that and waited for the rest of my friends. A fishing boat turned up and we screamed for help."

Mr. Watson had had the boat for only three weeks.

Luckily for the four the crew of the passing fishing boat, the Phillip F, who pulled them out of the river, spotted them.

Thanking those who came to their aid, Mr. Watson said: "We were very lucky that the boat arrived. We were only in the water for about ten minutes.

"Obviously we would have been there a lot longer if help hadn’t arrived. We could have been in the water for hours."

Fisherman Stevie Easterbrook, 21, of Richmond Road, Ipswich, was in The Phillip F with owner Barry Seeley, of Rickinghall, when they heard cries for help.

They saw three of the men clutching the mooring rope of the fishing vessel while another had managed to clamber on the back of the boat.

Mr. Seeley said: "I was just getting the ropes ready when we heard screams in the water. One of them was in a bad way and didn’t have any strength to even let go of the rope to which he was clinging.

"We went over and picked them up out of the water and got them out of their wet clothes.

"After the boat had overturned they swam back to it, until they realised it was sinking." The crew also rescued their possessions.

The Harwich inshore lifeboat also attended on Saturday night and escorted the fishing vessel into the marina, where Felixstowe Coastguard and an ambulance met it.

One of the men was treated at Ipswich Hospital after swallowing river water – but he was released that night.

A Coastguard spokesman said the four men were lucky to have been spotted and that they could have died if they had been in the river a long time