By Charlie Conchie Activist investors are gearing up for an offensive in London, and boardrooms across the City are scrambling to shore up their defences. In October last year, one New York hedge fund revealed a stark and telling bet on the UK’s public markets. Saba Capital, an investor with some $4.4bn assets under management known for waging campaigns from its Chrysler building HQ, had amassed positions in 11 different London-listed investment trusts in the previous 12 months. The price dislocation in UK-listed investment trusts is well covered. Scores of London-based vehicles are trading at…