The Port of London Authority has issued a message to boaters – stay off the Thames on Sunday unless you are part of the Diamond Jubilee Pageant.

It comes after fears that some jet skiers and small motor boat owners are  planning to take to the water and attempt to accompany the flotilla downriver.

The PLA’s Chief Harbour Master David Phillips said: ”I must emphasise the [tidal] river is closed on June 3rd to all boats except those involved in the pageant.

"We have had a lot of jet skiers and some owners of small boats threatening to come along on the day but that will not be possible

"If they do attempt to take to the river they will be spoken to by our staff. If that fails there are 24 police boats on the river who will back up our marshals – but we hope it does not come to that.

PLA Chief Harbour Master David Phillips

"Over the past few days we have a number of phone calls from jet skiers threatening to join in. My message is ‘enjoy the pageant - but from the riverbank.’ ”

Every member of crew and all passengers on the boats taking part have undergone a police security check.

Scrutineers from the PLA and the Marine and Coastguard Agency will also check every one of the 1,000  boats taking part – for sea-worthiness, and to see if the skipper has been drinking.

In an interview with River Thames News Mr Phillips said: ”Our message is very firmly ‘Don’t Drink and Drive’ on the river.”

Meanwhile normal maritime procedures for rescuing a person who has fallen overboard are being suspended for duration of the pageant. Usually a boat will stop, circle the spot where the person fell over and attempt to recover them.

But skippers have been told this could disrupt the pageant. Instead they are advised to alert a nearby rescue boat.

Mr Phillips said: ”Our advice if this were to happen is to raise the alarm but not attempt a rescue. We have told skippers not to attempt a recovery [in the normal way]. There is not the space within the flotilla and this will invariably lead to a collision and possible further casualties.”

The boats are being accompanied by 15 RNLI lifeboats plus marshalling and workboats which will carry out a rescue if needed.