As Greater Manchester faces a looming housing crisis, one company is challenging the perception of the long-term rental market. : As Greater Manchester faces a looming housing crisis, one company is challenging the perception of the long-term rental market. Sigma founder Graham Barnet has strived to create a new model in which institutions and wealthy individuals invest in residential developments - a first for the UK property market. Working alongside house builders the Scotsman has pieced together millions of pounds of investment to bring his vision to life.