Who owns the street? That sounds like a dumb question – it’s the city council, of course: it’s public space. That used to be generally true, more or less, but not so any more. Increasingly the responsibility for public space is divided in different ways between the municipality and private interests.

On one hand there is straightforward privatisation. When the Bullring and Brindleyplace were developed, the city council was happy to do a deal in which the developers purchased public streets and made them into private space. It meant that the council no longer had the expense of maintaining and lighting them. When you walk through Brindleyplace Square or Rotunda Square, you may feel that you are walking through public space, but you are not. It’s privately-owned space into which the public is allowed to enter, and it is policed by private security staff, not West Midlands Police.

How public it feels is partly a matter of design, partly the consequence of rules set by the developers for what behaviour they will allow in their space. Argent plc has fairly liberal rules for behaviour in Brindleyplace, and while the place may seem a bit artificial, it does feel friendly. When the Bullring was opened in 2003, the Birmingham Alliance, extraordinarily, prohibited visitors from taking photographs. This peculiar restriction was later dropped.

More recently, we have seen the introduction of a different hybrid, the Business Improvement District (BID). Initially conceived in north America in the 1970s, it took quite a time to be imported here in the UK, and was enabled by the Local Government Act of 2003.

A BID is an urban area, predominantly occupied by business, manufacturing or retail uses, in which the occupants choose to band together and pay an annual levy, which is then used to fund improvements and initiatives. There has to be a majority vote of businesses in favour of setting up the BID, measured both in terms of number of businesses and in terms of total rateable value. The BID then exists for a five-year period, after which there has to be a re-election.

Birmingham has one of the greatest concentrations of BIDs. There are five suburban ones – Acocks Green, Erdington, Kings Heath, Northfield and Sutton Coldfield – and five city centre ones – Broad Street, Colmore, Jewellery Quarter, Retail, and Southside. The total is about to become 12, as businesses in Soho, and Sparkbrook and Springfield have just voted in favour of becoming BIDs.

It is possible to take a cynical view of BIDs; a way for a cash-strapped local authority to pass costs on to the private sector, and a way for the private sector to serve its own self-interest at the expense of the wider community. Or more positively, one can see BIDs as a form of micro-local democracy, in which resident businesses can actively express a sense of ownership of their patch, developing both local distinctiveness and initiatives which are for everyone’s benefit.

The Colmore Business District (CBD) certainly seems to support this positive reading. It covers an area stretching from Chamberlain Square to the Children’s Hospital, and from Great Charles Street to Cannon Street. It was created in 2009, and its first five-year term ends next April; voting for a second term is taking place now.

It is of course one of the wealthiest districts in the city, containing a lot of banks, accountancy firms, property surveyors, and so on. But I write about it here because it is also one of the most publicly populated parts of the city, most of it within the Colmore Row and Environs Conservation Area, with many fine streets and much historic architecture. What has CBD added to the quality of urban life here?

Much of CBD’s programme is directed towards improving the public realm. Of the projected £4.1m budget for its second term, it plans to spend £2.2m on streets and squares. It doesn’t have any special rights over the streets: it has to work in collaboration with the city council, but it can significantly set the agenda. Improving public space clearly serves the interests of those who work in the district (and increases the value of their property): but it also benefits citizens and visitors who use the city centre less regularly.

The most visible evidence of the CBD’s engagement with the public realm is Church Street Square. This is the part-pedestrianisation of one block of Church Street, designed by landscape architects Capita Lovejoy, and completed last year. (An interesting comparison, which perhaps illustrates the effectiveness of CBD, is with Golden Square in the Jewellery Quarter. The same designers won the design competition in 2009. It’s still a car park).

Church Street Square is a pleasant hard-paved space with seats and trees, which provides a welcome social focus in the financial district. The street slopes quite steeply down from Colmore Row, and the different levels successfully reduce the scale of the space. Car parking spaces were removed to accommodate it. CBD’s attitude towards the motor car is rather equivocal: CBD has promoted the use of public transport, cycling and a car-sharing scheme, but it recognises that many of its affluent members still expect to drive into the city centre.

The next design project is to improve Colmore Square. This will be paid for entirely by CBD, with £300,000 of its own money, and will start next month. The Tom Lomax fountain displaced from Centenary Square by the new library will be relocated there. After that there will be improvements to the unsatisfactory space outside Snow Hill Station (a space not only sterile but even lacking a name).

Good places enable good events to happen there, and CBD has brought in beneficial cultural activity to the district: the Food Festival was imported here from Cannon Hill Park, the Jazz and Blues Festival takes place here, and much else. Can a BID contribute to the quality of public life of a city? It seems so.

* Joe Holyoak is a Birmingham-based architect and urban designer