A historic building at the heart of Birmingham's industrial heritage is set for a new chapter as offices and residential accommodation.

The Assay Office has been housed in Newhall Street since it was constructed in 1878 but staff and archives will soon move to a new purpose-built base across the Jewellery Quarter in Icknield Street.

New plans have now been lodged to convert the Grade II listed building into 30,000 sq ft of offices and 32 one- and two-bedroom apartments with private gardens and parking.

The project has been designed and submitted by city firm Glenn Howells Architects on behalf of property group TCN UK which acquired it last year.

Subject to planning permission, the intention is to start work on site in the autumn and for the offices to be operational by next spring.

TCN UK director Richard Pearce said: "This is our first project in Birmingham and it has been vitally important for us to identify the right building to invest in and create a vibrant and inspiring place where people want to spend their time.

"Alongside the physical presence of the building, we aim to create an atmosphere, brand and profile for our buildings and to develop a culture of collaboration and knowledge sharing which really does benefit our occupiers and their businesses."

The Assay Office has been extensively extended and adapted from 1890 through to the mid 1970s and was awarded Grade II listed status in 2004.

TCN UK said the proposals for the conversion were sensitive to the heritage and industrial characteristics of the building yet aimed to use the space efficiently to offer new occupiers the opportunity to personalise their own environment.

The apartments will range in size from 448 sq ft to 805 sq ft.

The façade and many of the internal historical features of the original building have been incorporated into the plans while Glenn Howells Architects' design has also utilised the 3.8-metre floor to ceiling heights.

The practice's studio director Michael Cruise added: "The Assay and its anchor hallmark are fundamentally associated with Birmingham's strong heritage within the silversmithing industry.

"Our design aims to retain the character of the existing building but to future proof it for modern working methods.

"The new build residential scheme will complete the missing corner of St Paul's Square and, through careful consideration of scale, materials and detailing, provide a design that is contemporary yet sensitive to the heritage context of the Jewellery Quarter."

Knight Frank has been appointed as residential agency.