A little-watched computer in the corner of Deutsche Bank’s London trading floor beeps. Then it does it again and again. The terminal, which registers corporate bond trades conducted on an automated system with the bank’s vast retail network, used to alert dealers to trades only occasionally. These days, however, the beeping is constant.

In the middle of this year’s bond-buying boom, which has already taken some measures of new issuance past full-year records, a new player is generating a lot of interest. European retail investors are buying bonds directly, many for the first time.