Co-locating libraries is an idea that is doing the rounds, and has been for some time. However, I am not sure that forms of co-location are fully appreciated.
A lot of Councils are seeing it as a way of saving money, an understandable approach in current circumstances. Sharing the costs of a building with different agencies can reduce costs, but if the space given over to each service is smaller that can lead to a worse service. It should be possible to avoid that through good design, but it remains a danger.
A second possibility is that it can be seen as a way of closing a library without making that quite so clear. When I heard of Barnet's former plan to "merge" libraries, I could not help but think that this was intended as a cynical PR manoeuvre. The trouble with such attempts is that people are unlikely to be fooled for long.
The real value of co-location, in my view, come from the very juxtaposition of services helping each attract higher footfall. Brent's new civic centre should be a prime example of this. People who would not normally go to the library serendipitously turn up, because they are in the building to attend one of the other services.
All this is pretty conventional, but it strikes me that there are effective forms of co-location that are not thought of as such. Temporary events held in libraries, such as the various Brent Dance Month events, have a similar effect. They draw in people who might normally attend libraries, but find the library more familiar once they have been there, and may come back. Of course, many may not, but it is effectively a form of marketing for the library.
A similar logic applies the library going outside. Brent libraries do this when they have stalls at outside events, but also through the outreach service. Although the refurbishment of Kilburn Library gave us a temporary hit in numbers, I think the outreach that went on there was an effective way to advertise the service to audiences that are not normally library users.
Both of these seem to me to be effectively forms of co-location, although they are not normally regarded as such.