A policeman has suggested the deaths of three British holidaymakers in Portugal could have been avoided if they had chosen a beach supervised by lifeguards.

Reis Aguas, commander of the maritime police in the South, based in Faro, was speaking after the Britons drowned trying to rescue their children off Tonel Beach in the village of Sagres on Monday.

Robert and Deborah Fry and their friend Jean Dinsmore, from Wootton Bassett, died after being caught in a treacherous current and a German father died of a heart attack after his child was saved.

There was no lifeguard on the beach at the time as it was not supervised following the end of the summer season.

But Mr Aguas said: "In the Algarve we also have more than 30 beaches where we have lifeguards.

"Even in the summertime we have some beaches with no lifeguards and people must choose the beaches which have a lifeguard - more if they have kids or aged people."

When asked about the lack of a sign to warn - in English - about possible dangers, he replied: "Do you in England usually have a sign in another language? In Portuguese?"

He said the rescue boat arrived at the scene within 17 minutes of taking the call.

Surfers and body boarders who took part in the rescue estimated the boats did not arrive for 40 minutes, by which time three of the bodies had already been dragged on to the shore.

The Frys' children - Rosie, 11, and George, nine - and Mrs Dinsmore's husband Roy, daughter Lydia, 11, and son Alexander, nine, survived the tragedy.

A family member said the children were "coping remarkably well" and helping to comfort each other.

A spokeswoman for the Attorney General's office in Lisbon said: "The public prosecutor has opened an inquiry and ordered the autopsies to be done.

"The object of the inquiry is not yet totally defined."

Mrs Dinsmore's heartbroken brother Johnny Morris, 45, from Herefordshire, said the four children were being looked after together and were doing "absolutely fine".

"Roy seems to be doing well because he's keeping busy. He's been unbelievable and is coping remarkable well. He's being helped by two friends they went out to Portugal with and they're all comforting each other."

Mr Morris, who runs the family's cattle farm in Willersley, said the families would not have ignored warnings the sea was too dangerous to venture into.

"If Jean was aware of any dangers to her children there's no way she would've gone anywhere near the water.

"It's just a terrible, terrible, tragedy. People can read things into it and find scapegoats, but it was an accident. No one was to blame.

"Hopefully lessons can be learnt from it and warning signs can be put up in future."

The Algarve Tourism Board said it was keen to co-operate with local authorities and would be willing to help finance new warning signs along the coast.

Mr Morris said: "As I understand it, Alex and Lydia hadn't gone out far and were pulled straight out.

"It was the other children they were trying to rescue. They were their best friends so that's what they would do to help them.

"Jean was a triathlete and a very strong swimmer. The currents must have been absolutely horrendous."

Alex Dinsmore's 10th birthday is on Saturday.

The father-in-law of Mrs Dinsmore, Keith Dinsmore, from Gillingham, Dorset, said his son, Roy, told them about the tragic incident by telephone on Monday night and broke down in tears.

"He was not clear about the details, but said they had been on a beach when the children got into difficulty.

"Jean must have gone in because she was an accomplished swimmer. She was a stronger swimmer than Roy and she did triathlons.

"Roy said he also went in and he and another man were injured with cuts and bruises."

He said Jean, a qualified part-time accountant, was "the best daughter-in-law you could ask for".

A steady stream of well-wishers have signed a book of condolences at St Bartholomew and All Saints Church in Wootton Bassett.

One message read: "You were such lovely, gentle parents. Always involved in your children's activities. I know you will watch over them in your own way as Rosie, George, Lydia and Alex grow. Heartfelt sympathy and love, Kate Stoney."

Flowers had also be left outside the two families' homes, which were at either end of the same street in the town.

A note pinned on a bouquet of flowers outside the Frys' house said: "Rosie and George, your friends are here to listen, to help and just be with you, doing ordinary, special things. With love and prayers Rhona and Chantal."

A spokesman for Portimao hospital said Dean Plumb, 40, the last remaining casualty in hospital following the incident, is being still being kept in as a precaution.

She said he remained "physically okay," but she did not know when he would be released.

Mr Plumb was one of three adults who required hospital treatment.