"What I love about this business," he says, "is that it's constantly changing - and you have to change too. As soon as you start telling old codger stories about the good old days, you've had it."
Harkness was elevated to vice-chairman of Barclays Capital in February, a promotion that chief executive Robert Diamond said reflected Harkness's "multi-faceted" role both with clients and in the firm's government bond business.
Certainly there's been no shortage of variation in Harkness's career. He reckons he must be one of the few people in the City who has worked as a stockbroker (for gold shares), in the futures pits, in a discount house and as a stockjobber. But then you also won't Find all that many Financiers who can run through an authentic Maori war dance - a ritual Harkness learnt as a rugby player in New Zealand in the 1960s.
Harkness is modest and quietly spoken - although reputedly also a good man at a party.
He was born in 1949 in Christchurch, New Zealand, where his father was a stockbroker. A talented rugby player, he played Flanker for both Christchurch and Canterbury (the province). After school he spent a year as a VSO in Fiji, and a further 18 months in Africa, which included a stint in the Financial markets in Johannesburg and six months running a hotel in the Kalahari desert in Botswana.