By Christine Jeavans BBC News Online

As the first good weather of 2002 tempts people and pleasure craft down to the sea, Christine Jeavans visits a coastguard station to find out how Britain's fourth emergency service operates. Somewhere in the 90 miles of cold grey water that separates Essex and Holland, a skipper is making a radio call he would rather he didn't have to make.

"Calling coastguard, coastguard. This is Venturer, Venturer. We are a four man dive boat and have engine failure."

Their inflatable power-boat is 30 miles off shore, it offers no protection from the elements and if the group cannot fix the engine, they have no way back to land without help.

It must be no little relief when the calming voice of Coastguard Watch Officer Catherine Boyer-Besant comes through the radio: "Venturer, Venturer, this is Thames Coastguard. What is your position?"

Missing children

For most of the UK, Saturday 1 June meant the start of a four-day weekend of World Cup football and Jubilee street parties but Catherine and her four colleagues of Thames Coastguard's D Watch are working their usual 12-hour shift.

Catherine Boyer-Besant: "You never know what will happen next"

From their operations room perched at the end of the beach at Walton-on-the-Naze, Essex, the team responds to any incident from Southwold in Suffolk to Reculver on the north Kent coast.

If a child is swept out to sea on an inflatable toy, a motor boat breaks down or a tanker runs aground, it is the coastguard who co-ordinates the search and rescue operation - 24-hours a day.

"You never know what is going to happen next," says Catherine, 33, who has been with Her Majesty's Coastguard for five years.

Almost 5,000 people were rescued last year

"The majority of incidents we deal with involve pleasure craft but in the summer every other call will be about a missing child.

"And at anytime you could be looking at a major incident."

Thankfully, those which end in tragedy are few and far between.

Thames dealt with 595 incidents last year. Seven people lost their lives but 268 were rescued.

'Breakdown service'

Catherine is on the radio again. Venturer has called back in to say they cannot fix the engine and require assistance.

There are no other vessels in the area to help out and it is evident that a lifeboat will have to go to their aid.

Plotting a vessel's position from co-ordinates

The coastguard describes itself as "the real fourth emergency service" - a dig at a certain roadside recovery company which also claims that title.

Ironically, coastguards constantly find themselves having to deal with the marine equivalent of a burst tyre.

"We are not a breakdown service," says Catherine, "but if we don't do something then a boat can drift or the weather gets worse, it gets dark and then the situation can turn nasty".

She puts in a call to the Walton lifeboat crew to request a launch to come to the dive boat's aid and within 15 minutes, it is ploughing out to sea.

Stricken yacht

In the operations room, things are getting busy for D Watch.

A speedboat off Herne Bay cannot get back to shore; a cargo plane logs a report of a large ship lying on its side and Dover coastguard is searching for a missing light aircraft.

Children on inflatable toys can float away in seconds

Then a faint call comes in on radio channel 16 - the emergency channel that all boats keep open in case of trouble.

A yacht has run aground on a sandbank just off Shoeburyness, the skipper is alone on board and he is worried the craft will be dashed against the bank.

Catherine reassures him that the tide is rising and he should re-float soon but the man's voice sounds shaky and it is unclear whether he needs further assistance.

Communication is lost. However, minutes later the man's wife rings up in a distressed state, saying her husband has called her on his mobile phone and is worried for the safety of his yacht.

The team call Southend Lifeboat crew who speed off to the stricken vessel.

Breaking bad news

"We often have to deal with concerned relatives, especially if they are non-sailors themselves," says Catherine.

"Most of the time we can reassure them - and usually they find their loved ones are safe in the local yacht club bar and have forgotten to phone home.

"But bad things can happen and we do have to break distressing news from time to time - which is awful for all concerned."

Fortunately, today's incidents end safely.

The yacht on the sandbank is towed back to harbour; Venturer and her four-man crew are also under tow back to Felixstowe.

And the "ship on its side" spotted by the cargo plane turns out to be a car-carrier, which is very much afloat.

But just when things appear to be quietening down, the radio crackles again.

"Hello Thames Coastguard," Catherine responds.

"How many are on board.... do you have an anchor down or are you drifting?

"OK sir, we will see what we can do to help."