The patient, known as Patient A, had suffered ill health after taking part in a clinical trial and was in the process of filing an injury claim when his lawyers advised him to see Prof. Johnston for expert advice.
Today, the angry patient accuses the doctor of over-charging, dishonest about the time spent consulting and failing to examine him.
He reported the specialist to the Heart and Lung Institute, at Imperial College London and the General Medical Council (GMC) and now, Prof. Johnston is facing a tribunal.
Part of the evidence presented at the tribunal include a CCTV footage of the patient which allegedly shows him arriving home in a taxi just 70 minutes after it was agreed the consultation had started.
Despite being confronted with the CCTV, the Professor Johnston accused the man of doctoring the footage.
In an email, he said: 'I should charge for the further time spent as it is taking up a great deal of my time.'
Professor Sebastian Johnston, 56, filed an invoice for his advice, claiming the £6,500 cost included the time he spent making a cup of tea, the medical tribunal in Manchester heard.
He gave a breakdown of the bill, including charges of £600 (N150,000) an hour for his expertise and saying the meeting began at 2pm and took two-and-a-half hours.
Professor Johnston, who is also an honorary consultant physician at St Mary's Hospital in London, denies that his invoice was 'grossly inaccurate' and dishonest.
The hearing continues until Friday December 4, after which tribunal will produce a statement on its decision.
WOW! £600 per hour.....That's almost a doctor's monthly salary here.