The 27-year-old, fourth at last summer’s Olympics, pulled clear of rival Aimee Wilmott to win in 4 minutes 34.12 seconds with Aberdeen training partner Orla Adams seventh.
But Miley will now have to wait on selection for Budapest after finishing an agonising four-hundredths of a second outside the automatic qualifying time despite fighting off a crop of fresh contenders.
“I’m a bit tired,” she admitted. “But it was great to see a lot of the youngsters coming through in the morning’s heats, who can go under 4:40. It made me excited to race the final. It means the event’s moving on and hopefully dragging me along with it.”
Ross Murdoch had to play second fiddle to Olympic champion Adam Peaty in the 100m breaststroke, with the Englishman romping clear in 57.79 seconds at Ponds Forge to become the first person to officially book their ticket to the worlds.
Scot Murdoch, who will race over 200m later this week, was over two seconds behind, with Stirling team-mate Craig Benson fourth but Peaty was simply unstoppable.
He was also in a generous mood, giving away his latest gold medal to a 10-year-old boy in the crowd. “Hopefully that medal will inspire him every day now,” Peaty said.
James Guy landed a third successive British title in the 400m freestyle as fellow Olympic silver medallist Stephen Milne taking silver.
Edinburgh’s Corrie Scott took bronze in the women’s 50m backstroke with Imogen Clark winning in a UK record of 30.21secs. Craig McNally was third in the men’s 50m backstroke behind Chris Walker-Hebborn with City of Perth’s Scott McLay taking the junior title in the event to boost his chances of a swim at this year’s world junior championships in Indianapolis.
Duncan Scott debuts in the 200m butterfly today while Kathleen Dawson will open her championships in the 100m backstroke, with the European medallist looking to show the steps forward made since her switch to Stirling last autumn.
“It will give me more confidence in myself,” the Scot said. “I’m already happy with how things are. I know I’m world standard and that I can compete against these girls who went to the Olympics. Worlds is my next target. And now I have to be ready to take that one.”