McFarlane said that the the bank's board members had rated his chances of executing Barclays' new agenda as higher than Jenkins.
"He (Jenkins) was good at executing what we asked him to do at that time. What we are asking him to do now is different and the board believes that the probability of my executing is higher," McFarlane told CNBC.
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He added that it was "perfectly obvious," there were a "number of issues" at Barclays.
"One is that it is a very clunky type of organization," McFarlane said.
"It's not fast-moving; it's not lean; it's not agile—it is with customers, but it isn't in terms of execution. Our efficiency levels are low, our capital is being used in the wrong way and we really need to deal with that and very quickly and bring it forward."
Jenkins, who took over in 2012 after a scandal over the bank's fixing of the key Libor interest rate led to the resignation of predecessor Bob Diamond, has overseen tough times at the bank.