Focus: Richer than the Queen (and considerably better connected)

They call her the Gilded Lily. She is said to be the world's wealthiest widow, with a fortune estimated at £700m. In comparison to 65-year-old Lily Safra, even the Queen looks hard up, and rather less well connected.

Driven round London in an enormous armoured BMW, Mrs Safra is protected 24 hours a day by a posse of bodyguards and by sophisticated security systems at her six-storey, £23m home in Eaton Square.

Four years ago, she was barely known in Britain. Today, she is among the most powerful people in London's social and philanthropic circuits. She has become friends with the Prince of Wales, lavishing money on his charity, The Prince's Trust, and rubs shoulders with Camilla Parker Bowles, Lord Rothschild and Sir Elton John.

Mrs Safra's influence is more significant than a few mentions in the diary columns. She is changing the tone of London. Under her influence, it is becoming more like New York, where social position is defined not by what you have, but by how much you can afford to give away to worthy causes. For instance, she donated £8m to Somerset House for the computer-controlled fountains in its magnificent courtyard, and managed to arrange, against fierce opposition, for it to be named after her late husband Edmond, a banker.

But such a rapid social conquest, proof, if it were needed, that money buys access to the highest levels of London life, is threatened by the trial being held in Monaco of the American male nurse who is accused of killing her husband in 1999.

This week, Mrs Safra takes the witness stand, and high society across Europe is salivating at the prospect of any number of possible revelations about the Safras' rarefied world of private banking billions. Throw in mysterious clients, bumbling police, a socially ambitious widow, and the highly charged atmosphere of Monte Carlo and you could hardly hope for a more enticing mix.

Ted Maher, 44, who had been hired to help care for Mr Safra, who suffered from Parkinson's disease, has admitted he lit a fire in a waste-paper bin in his employer's Monte Carlo penthouse. He hoped to win Mr Safra's favour by pretending they were being attacked, then "save" him. But the fire raged out of control.

Mr Safra who believed assassins might be behind the fire, died with another nurse after refusing to leave his locked bathroom. His wife, who pleaded with him to leave, escaped unharmed.

There have already been wild allegations that Mr Maher's wife was kidnapped by the Monaco police, and unfavourable comments that two out of Lily's four husbands have died in mysterious and tragic circumstances. She has also been sued by Mr Safra's three sisters over £14m they believed was owed to them from his will – although that is now resolved – and has fallen out with his brother.

There have even been murmurings about whether Mr Safra's great friend Prince Rainier intervened behind the scenes in a cover-up because he wanted to protect his principality's tax-haven reputation.

Questions have been asked about why Mr Safra's usual round-the-clock bodyguards were told to take that night off. And where are the security videotapes that should have recorded what happened?

So concerned is Mrs Safra at any possible further damage to her standing that she has hired the services of Prince Charles's spinmeister Mark Bolland (on the recommendation of Camilla and Lord Rothschild) to handle her image. He is already paid £120,000 a year by the prince for part-time PR consultancy, but he is expected to make much more from her.

It is all a far cry from her early days as Lily Watkins, the daughter of a Russian Jewish émigré, she tells friends, who made a modest fortune exporting British railway carriages to Brazil. Conflicting reports about her childhood suggest she was born in Mitcham, Surrey, or in Uruguay.

What is known is that she speaks five languages – English, French, Italian, German and Portuguese, and is working on Russian – and that she acquired her wealth from her four husbands. She speaks English with an indefinable foreign accent. She "charms charmingly" say even her critics, and one friend describes her as "a serious, clever, quite devout but tough person, not silly or giggly, who has dressed in sombre clothes since her husband died".

Another acquaintance said her determination to retain her youthful looks had left her face "with wide-open eyes and a slightly strange look that makes it difficult to tell exactly what age she really is. She has also taken to wearing a lot of black eye make-up recently".

Still X-ray thin – and fond of sporting a quantity of costly diamond and platinum jewellery – she started married life with Mario Cohen at 19, and they had three children. Then she became Mrs Freddy Monteverde, wife of a Brazilian hosiery magnate, who, says Brazilian police, committed suicide because he was depressed. He left her with £160m, but there were also unhelpful stories that Mr Monteverde had mysteriously shot himself twice in the heart and police had not arrived on the scene for almost seven hours.

A quick third marriage followed, but Mrs Safra had already turned to Edmond for financial advice. They married in 1976 and lived in a sumptuous six-bedroom apartment on Fifth Avenue in New York, with a guest suite at the Pierre Hotel for friends. Mr Safra, a Lebanese-born Sephardic Jewish financier whose private bank attracted a mix of clients from royalty to film stars, had always led a quiet, workaholic life but his fashionable new wife soon became a leading player in the socially competitive charity circuit in Manhattan. Society began commenting on their "meteoric rise to social power".

Status was important; the Safras wanted the social cachet enjoyed by the Rothschilds. After all, the couple – worth an estimated £3bn – had all the required material trappings of the mega-rich, including their lavish hilltop mansion La Leopolda, which is claimed to have the best sea views in the south of France. It was built by King Leopold of the Belgians in the style of a Roman villa.

Since the death of her husband, Mrs Safra has continued to entertain on a lavish scale at any of her homes across the globe. Fortunately, Mr Safra reportedly changed his will shortly before he died, leaving a large part of his fortune to her, as well as to his charitable foundation. As long as she can get this lurid and exotic trial safely behind her, there will be no stopping her remorseless scaling of the social heights.