Social Change and Immigration

This clip from the Today programme on R4 gives a great bit of social reportage. Listen especially to the interview with the market stall holder. It poses a number of interesting questions:

Is this an accurate picture of migration into and out of the area? (it’s only a few interviews)
Why have people moved?
Where have the ‘white’ population moved to?
What happens to culture and identity in times of high levels of migration?

In a way, you could say a report like this is like a piece of small-scale sociological research. What are the advantages and disadvantages of the interview technique for investigating large-scale and long-term social change?