By Charlie Conchie Companies listed on London’s junior AIM market are being told to prepare to flee the exchange or announce emergency share buybacks amid fears that a punishing inheritance tax raid could trigger a sell-off, City AM has learned. In a letter seen by City AM, one investment bank has urged all of its AIM-listed clients to prepare “proactive measures” ahead of the budget on 30 October to cushion themselves from any turmoil sparked by the Chancellor Rachel Reeves’ rumoured plans. Shares on the market currently enjoy a tax-break which exempt them from inheritance tax if they have be…