This is one of the most wonderful drainpipes and hoppers I've noticed. It's on the main post office in York, which is a rather nice Victorian building altogether.
The building was designed by Sir Henry Tanner, probably the Post Office's best-known architect. The year York Post Office was built, he became principal architect of HM Office of Works (the department responsible for designing most main post offices of the period). His post office work can be seen throughout the country, and included major London buildings such as the King Edward Building in St Martin's-le-Grand.
Further reading: British Post Office Architects is full of information on both post offices and the people who built them. The British Postal Museum and Archive has published Built for Service: Post Office Architecture by Julian Osley.