The document, which asks shareholders to support Mr Rowland in his fight to become president of Lonrho at the annual meeting next week, makes a series of allegations about Mr Bock's conduct since his arrival at Lonrho in 1993.
It says that Mr Bock tried to persuade Mr Rowland to accept a stake in his German holding company, Advanta, in payment for the shares in Lonrho that he bought from Mr Rowland.
It accuses Mr Bock of selling Lonrho assets such as its holding in Krupp, the German company, at a knockdown price and of making only one, loss- making acquisition since he took over at the group.
In the letter, Mr Rowland also defends his business dealings with Libya, his feud with the Fayeds over the sale of House of Fraser and his salary and perks such as the private aircraft he used while at Lonrho. He goes on to threaten to call an extraordinary meeting by the end of the year and says: "My services to Lonrho cannot be terminated since they come from the heart, and perhaps you will consider recognising whatever fun and profit you have had from your shareholding in Lonrho by voting for me, too."
A spokesman for Lonrho described the allegations in Mr Rowland's letter as "complete rubbish".
"Mr Rowland states in the letter that he had made many mistakes. This is one of them. His allegations are inaccurate and spurious. It is all rather sad, and the board, which met this afternoon, are entirely ignoring it."
Mr Rowland says in the letter that he composed it after a telephone conversation with a shareholder who summed up the criticisms that have been made against him.
He explains that he fell out with Mr Bock after he refused to accept Advanta shares as payment for the stake in Lonrho he sold to Mr Bock. He claims Mr Bock tried to persuade him on a trip to Russia and that when he refused "all smiles ceased". "Since that day I have received two telephone calls from Mr Bock."
Mr Rowland also criticises Mr Bock's choice of non-executive directors for Lonrho, adding a swipe against Lonrho's spokesman, Anthony Cardew of Cardew and Co.
"Mr Stephen Walls has recently become involved in running a frozen food company called Albert Fisher whose share price today at 40p is the lowest for two years. He was recommended by Anthony Cardew, your company's new `public relations' man."
"Quite apart from my personal feelings over broken promises and broken agreements, I objectively consider that Mr Bock has displayed very poor management skills in the last 18 months."Reuse content