Private-equity firms more than tripled the value of U.K. purchases in the past 12 months, according to the accounting firm BDO LLP. They exploited a collapse in the pound and skittishness that had firms such as Sanford C. Bernstein calling British equities uninvestable amid the political chaos. “Over the last 12 to 18 months we have seen a significant increase in interest from our clients in pursuing public-to-private deals,” Kem Ihenacho, the global vice chair of the law firm Latham & Watkins LLP’s private-equity team, said in an interview.