Private equity investors are very interested in professional services businesses spanning industries like law, consultancy, and finance right now – and there is perhaps no better organisation to depict such fervent desire than Grant Thornton. In the space of five months, the American and Irish franchises of the tax and advisory business network have been the subject of significant investments that could somewhat dilute the partnership model that has defined the industry for decades. In May, New York investment firm New Mountain Capital bought a majority stake in the US arm of Grant Thornton. New Mountain was joined by Canadian…