Plymouth Leander star Proud, who won the BUCS Championships in February, had eased through Saturday morning’s heats and despite having to swim five separate races in the evening he had enough stamina to hold off his rivals to take victory in the knockout competition.
The double Commonwealth Games sprint champion will be hoping for more success on Sunday when he competes in the 100m freestyle event.
There was also success in Edinburgh for former Kelly College pupil Cameron Brodie.
Scottish international Brodie, now at the University of Stirling, won the 200m butterfly race, beating American short-course record holder Tom Shield.
Brodie said: “It’s one of the best fields I have been up against and it’s nice to get that win in before the trials.
“Racing is massively important a month out from the trials.”
April’s British Championships will be trials for the World Championships, the European Games and European Junior Championship teams.