The market capitalisation of Tata Group's companies has fallen further. This is amid the ousted chairman Cyrus Mistry's recent email to the Tata board.

In the email, Mistry warned that the conglomerate risked up to $18bn (£14.7bn) in write-downs. He said this was amid the group's five unprofitable businesses. He added in the email that he had inherited a group that had a lot of debt and loss making businesses that were running for emotional reasons.

He also said that his chairmanship had been undermined and that he had been pressurised into doing deals that he was not comfortable about. "Apart from the invalidity and illegality of the business that was conducted, I have to say that the board of directors has not covered itself with glory. To "replace" your chairman without so much as a word of explanation and without affording him an opportunity of defending himself in a summary manner must be unique in the annals of corporate history," the email as cited by the Times of India, read.

On Monday, Tata Group had announced that its chairman Cyrus Mistry had been removed from his post with immediate effect to be replaced by his predecessor Ratan Tata. Tata Sons, the holding company behind the Tata Group, said the decision was taken at a board meeting in Mumbai on 24 October. It had, however, then not given the reason for its decision.

Since Monday, the group companies of the Indian conglomerate have been in decline. According to a Livemint report, these companies had in total lost more than Rs 270bn (£3.33bn) in market cap over three days. On Thursday, Tata Steel had closed at Rs 397.15, down 0.36%, while Tata Motors had closed 1.52% lower at Rs 522. Shares of Tata Consultancy Limited was, however, marginally up 0.91% at Rs 2,418.10.

Apart from these three major companies, the group has many other companies listed on the Bombay Stock Exchange. These include, Tata Chemicals, Indian Hotels, Tata Metaliks, Voltas, Rallis India, Tata Elxsi, Tata Global Beverages and Tata Communications among others. The share price of all these companies had closed lower on Thursday.

Amit Singh, vice-president, institutional equities, at Choice Broking, said these companies could see a further slide in their stock prices, going forward. "We see further pressure in stock prices of the group owing to recent developments of write off possibility suggested by Mr Mistry, especially since the exchanges have taken up this matter with the group," he said.