The extraordinary scene was provoked by an article 61-year-old Miss Robinson wrote in February last year. She claimed in a column in The Daily Telegraph that Miss La Plante could not be 57, but must be at least four years older, 'cruising nicely towards 62'.
What's more, she claimed she knew Miss La Plante when she was Lynda Titchmarsh and growing up in the Lancashire seaside town of Blundellsands.
Noting reports about her age, Miss Robinson said: 'I thought, "That's a bit odd", because she was best friends with a girl who used to live opposite me called Elaine, who was 11 at the time and Lynda was the same age, as was my brother.
'Elaine and my brother are now pushing 62. If Lynda is right, she would have been six and it would be very unusual for an 11-year-old and a six-year- old to be best friends. It seems strange that Lynda is now two years my junior.'
But last night Miss La Plante spoke of the trauma which spurred her to accost Miss Robinson.
'Her comments had a devastating effect on me and could have had a devastating effect on the most precious thing in my life, my son Lorcan,' she said.
'The suggestion that I had lied about my age could easily have harmed the adoption process because I could have been accused of being less than truthful.
'The remarks triggered a total invasion of my privacy and some unbearably nasty vitriol about me in the media. It was the most stressful time of my life.
'I always said to myself that if I saw this woman I would confront her to say how flippant her article had been and how incorrect.'
Last week Miss La Plante and Mr Massow were dining at the Ivy when Miss Robinson walked past their table.
'I thought I would introduce myself. After all, she claimed she knew me and I know we have never ever met. I did think of tipping spagbol over her but Ivan talked me out of it because it would be undignified.
'I was exceedingly polite but I found it quite nerve-racking to confront someone who had caused me so much stress.
'I wanted to tell her she had instigated a lot of unpleasant things and I had no idea why. People even tried to dig up the identity-of my son's birth mother. What her article did was inspire virtually every woman newspaper columnist to say it was appalling that a woman of my age was being allowed to adopt.
'I had to do what I did. Everyone should confront things - and behave decently.'
