Friends and family of Mrs Barrantes will gather at a church in Buenos Aires for the service on Thursday evening.

Fergie and her sister Jane travelled to Argentina earlier this week after their 61-year-old mother was killed on Saturday.

The Duchess is expected to fly into Beunos Aires to give a reading at the memorial service.

Her spokeswoman said the service was partly for those who could not attend the funeral.

Duchess of York was greeted by a throng of media on arrival in Argentina

Susan Barrantes was buried on Tuesday in a vault next to her late husband Hector on the edge of a polo field on the couple's estate in El Pucara, 350 miles from Buenos Aires.

The local parish priest conducted a 30-minute service in front of a small group of mourners.

Argentine President Carlos Menem sent a floral tribute.

The Duke of York did not travel to Argentina for the funeral. He stayed in Balmoral carrying out private engagements.

There will also be a service of thanksgiving for her life in England towards the end of the year.

According to Argentine newspaper reports, the Rover 420 Mrs Barrantes was driving was travelling at 124mph when it crashed into a Renault Trafic van.

The Duchess's daughters Beatrice and Eugenie stayed at home

El Tribuno reported that police investigators had found the speedometer of the car stuck at 200kph.

It also emerged that Mrs Barrantes, who was 61, had been involved in another serious road accident a year before the fatal crash.

On that occasion her life was saved by her seat belt as her car overturned up to seven times.

A friend of Mrs Barrantes, German Sanchez, 24, told an Argentinian newspaper: "She drove very well but she used to really step on the accelerator - she regularly went at 150 or 160kph (93 to 99mph)."

Raphael Barrantes, Mrs Barrantes's 25-year-old nephew, survived Saturday's crash with minor injuries and left hospital on Sunday.

The driver of the Renault van was named as salesman Jose Maria Rodriguez, 60, of Tres Lomas - reported to be a close friend of Mrs Barrantes.

He remains in hospital with a broken right foot.