Further research

Use keywords and phrases, NOT full sentences. 

For example, a good search term is: 

identity and ethnicity and Britain

While a bad search term is:

what does ethnicity have to do with identity in Britain

Use filters to narrow down your results.

When you've stated a search, you'll see filters on the left side. Use these to narrow your results to see the most recent publications, or to see just articles, or just ebooks.

Use bibliographies (reference lists).

Found a relevant book or article? Use the bibiliography (the list of sources at the end of the work) to see what evidence the author used in their work, and track this evidence or authors down.

Think like a detective. 

Once you've started reading in your topic, identify the "big names" in that field or topic that keep coming up, and then research them.