SHANGHAI—A husband-and-wife team of foreign investigators based in China, Peter Humphrey and Yu Yingzeng, were formally arrested in recent days by police in Shanghai, according to a statement issued Wednesday by family members.

In a statement to The Wall Street Journal, the family said the two are suspected of breaking Chinese laws related to purchasing personal information. The statement said the two have lawyers and have been in touch with consular officials.

Mr. Humphrey, the British co-founder of ChinaWhys Co. and a former reporter with Reuters news agency, is among the better-known private corporate investigators in China. His ChinaWhys co-founder and wife, who goes by the name Ying, is a U.S. citizen and a California-educated accountant.

Mr. Humphrey was formally arrested in Shanghai on Aug. 19, according to a spokesman for the British Embassy. A spokesman for the U.S. Embassy in Beijing couldn't comment on Ms. Yu. He said clearance from Washington is needed before the government can update its statement from mid-July that said an unnamed U.S. citizen had been detained in Shanghai and that the consulate was offering the person assistance.

The two were detained by police, but not formally arrested, on July 10, the statement from the couple's family said.