Having bought The Mailbox, the former Royal Mail sorting office, next to the canal in central Birmingham, in April for £127.1 million from Birmingham Development Company in April 2011, Brockton Capital and JV partner Milligan Retail are now planning to invest a further £50 million in a major redevelopment.

A new roof, larger public areas and improvements to the surrounding infrastructure will be created, while allowing Harvey Nichols, which anchors the upmarket shopping at the Mailbox, to double it's size.

Presently the building consists of 640,980 sq ft of quality office, retail and restaurant space. Additionally, the site features a 686-space car park that spans 4.8 acres, and includes 144 residential apartments, 165 dedicated private parking spaces and two hotels that are leased on long ground leases in the estate.

Plans have been drawn up by architect Stanton Williams and work is set to begin in the summer and be completed by spring 2015.

A key part will be Harvey Nichols’ move to a new 45,000 sq ft store when the development is re-launched.

But the Mailbox’s owners are also keen to capitalise on the improved £600 million New Street Station and plan to invest in public areas outside to encourage greater footflow from the new John Lewis.

They are currently working with Birmingham City Council to introduce a new, improved pedestrian-friendly area around the underpass beneath Suffolk Street Queensway, improving access from Navigation Street and New Street.

The work will mean some disruption to trading; Jaeger, LK Bennett and Gieves and Hawkes will close for a period and return afterwards.

The former owners, Birmingham Development Company, went bust in 2010 building the Ken Shuttleworth-designed Cube development, which adjoins the Mailbox. Both building owe their existance to the vision of Alan Chatham, who bought the Royal Mail sorting office with partner mark Billingham for £4 million in 1998, and has a knack of turning muck into brass.