The largest mixed-use building in Britain besides London's Shard is back - and it's a lot more cutting edge.

It may share little of its status but the 95-storey London skyscraper is the only building in the country to compare to Birmingham's Mailbox, which is re-emerging after a £50 million redevelopment.

Such is its scale, that shoppers standing on the stairs of The Mailbox are actually closer to the new John Lewis behind them than the rear of the building.

Brockton Capital and partner Milligan, which bought the former Royal Mail sorting office in 2011, have invested in a new roof, larger public areas and improvements to the surrounding infrastructure.

The upshot is a grander space for luxury retail - principally in a 300ft long "urban room" on the second floor.

Brockton partner Simon Samuels said: "This asset needed whole-hearted transformation, not a sticking plaster.

"While all the focus has been on the retail position, it is also the offices, the food and beverage, everything - with mixed-use, everything has to feed one another.

"Birmingham's disposable income is more than in Manchester, Leeds, anywhere outside London. There are more millionaires here than in any of those other areas."

The old Royal Mail sorting office in 1998 before redevelopment commenced
The old Royal Mail sorting office in 1998 before redevelopment commenced

Mr Samuels said he had confidence that more visitors would flock to the city - but the challenge for The Mailbox was to ensure it was on the list of luxury destinations.

The expanded Harvey Nichols is central to the retail element but the new Everyman Cinema and Gas Street Social bar-restaurant have also been opened.

A new Armani store is also set to be fitted out.

The Mailbox project is by no means complete, as revealed by four empty stores fronting the urban room, and there is also a second anchor store underneath Harvey Nichols still to be filled.

But Mr Samuels said about three-quarters of the shopping space was let with at least four new retailers expected early in the new year.

There is also 45,000 sq ft of office space up for grabs.

Paul Hanegraaf, creative navigator of Milligan, said: "We want The Mailbox to be a place people go to, then decide what to do.

"There are places to dwell, somewhere to have a nice lunch, shop, or watch a movie. Before, it wasn't capturing enough people coming into Birmingham to shop for luxury. The idea is to capture a few more of them and suddenly it all looks better."

The most impressive part of the redesign is the new urban room, which stretches into the Harvey Nichols store.

Inside the new-look Mailbox
Inside the new-look Mailbox

Space, along with the drastically reduced prospect of being rained on, is the most fundamental shift.

Before, people merely using The Mailbox as a through route would rub shoulders with shoppers in a narrow concourse.

Now, the thoroughfare is kept downstairs while the urban room above has been turned into a more spacious affair.

One of the major changes is in technology. When visitors arrive, those who have signed up for the app will be registered as soon as their number plate comes into view.

Brockton and Milligan have worked with Mailbox retailers to sync with their digital output, so visitors might see the latest lines from designers they have bought from in the past or deals on meals in one of the restaurants.