The Cube has pulled off the office deal of the year in Birmingham after persuading the Solicitors Regulation Authority to make the distinctive building its new headquarters.

The SRA, which regulates solicitors across England and Wales, has been looking at a number of city centre premises, including Nurton’s 2 Colmore Square, before eventually choosing the Ken Shuttleworth-designed scheme at the back of the Mailbox.

Some 700 staff from both the SRA and the Midlands Law Society, currently working in three offices based across two sites in Redditch and Leamington Spa, will occupy 57,000 sq ft of the landmark building next summer.

The deal means that the entire 120,000 sq ft of commercial space at the Cube has now been let with the SRA joining the Highways Agency which moved into the building last year.

Despite being taken into administration in March 2010 by its principle funders Lloyds, the mixed use scheme has been an undeniable success story having let all its commercial space, sold the majority of its apartments and attracted a hotel with club and spa, a Marco Pierre White restaurant and an Adee Phelan salon.

Neil Edginton, who was a director at the scheme’s original developer Birmingham Development Company and was kept on to complete the project and help find occupiers by administrators PwC, said the SRA letting vindicated the original vision for the Cube.

He said: “For me it shows the worth of bringing in someone like Ken Shuttleworth to design something completely different for the city which has really got people talking and ultimately driven inward investment into the city.

"If you look at the Marco Pierre White deal, they came to the city because of the Cube. Now we’re delighted to welcome the Law Society and the SRA to what we firmly believe is Birmingham’s best business address.”

The past 12 months have been particularly challenging for the property community and while the number of deals are up year on year, there have been very few above 20,000 sq ft in the city centre making this the largest in the city core in 2011 by some distance.

John Griffiths, from GBR Phoenix Beard - who were joint agents for the Cube with DTZ while Knight Frank represented the SRA and Law Society - said the deal was great news for the Cube and the city’s office market in general.

He said: “I think there are certainly difficulties in delivering a truly mixed use building but the market likes the mixed use environment and if anyone is looking for an endorsement from an occupier point of view then this is it.

"It has been one of the most challenging years that any of us have seen but a fantastic way to finish it.”

The SRA, established in 2007, regulates more than 120,000 solicitors in England and Wales and offers guidance to help them act within a code of conduct while the Law Society is the independent professional body, established for solicitors in 1825, that works globally to support and represent its members.

Desmond Hudson, CEO of the Law Society, said: “Consolidating our four current Midlands buildings and all our Midlands-based staff together, under one roof, will reduce our costs, make us more effective and more efficient.

"The Cube offers us a better, greener and more centrally located working environment, topped with first class transport links. The move to Birmingham city centre demonstrates our long-standing commitment to the West Midlands.”

Antony Townsend, chief executive of the SRA, added: “The Cube offers us excellent facilities in the heart of Birmingham city centre to consolidate our position as the principal regulator of legal services, and to attract high-quality staff from a diverse population.”