LONDON, July 17 (Reuters) - British house prices rose for a third month in a row in May, increasing by an annual 2.2% after a 1.3% rise in April, the Office for National Statistics said on Wednesday.

The ONS's gauge of private rents increased by 8.6% in the 12 months to June, slowing slightly from May's 8.7% rise. (Writing by William Schomberg, editing by Andy Bruce)