Something went wrong, please try again later. Invalid email Something went wrong, please try again later. Sign up for our daily newsletter to get the day's biggest stories sent direct to your inbox Through a glass door next to a Chinese restaurant, in an anonymous 1970s office block above a barbers and a Greggs, lies Manchester's most secretive building. Heron House is home to signals intelligence agency GCHQ. Inside hundreds of spies carry out the clandestine business of keeping tabs on those who might wish to do the UK harm. Read more: Sir Iain Duncan Smith tells court of moment…