Turkish authorities stopped Waheed Ahmed, 21, and eight of his relatives near the Syrian border on April 1, The Guardian newspaper reported. The group, comprising five adults and four children, are all from Rochdale, Greater Manchester.
Ahmed was deported from Turkey late Monday and arrived in the United Kingdom in the early hours of Tuesday.
The police are "working to ensure the safe return of eight other people to the UK," a Greater Manchester police spokesman said, as quoted by The Guardian.
"If I thought for a second that he was in danger of being radicalised, I would have reported him to the authorities," Shakil Ahmed said in a statement.
Many of those who seek to join extremist groups in Syria attempt to do so by entering the country through Turkey. In March, a 21-year-old woman and, separately, three British girls were detained after arriving in Turkey illegally.
