Learmonth, from Berwick, finished in a superb fourth place in the UK 800m under 20 final, setting a new personal best of 1.49.23, which is just outside the world junior qualifying time of 1min 48.5.
The junior final was probably the best field ever assembled in the history of the championship with the first six runners all faster than the winner of the under 23 final.
Winner Nial Brooks, who was second in last year's European championships, ran 1.47.29, breaking the championship record previously held by Olympic finalist Ezekiel Sepeng of South Africa. In second place was Adam Cotton who dipped under the world qualifying time with a 1.48.30. In third place was James Bowness from Cumbria who, like Learmonth, finished just outside the world time.
The four athletes Brooks, Cotton, Bowness and Learmonth are four of the fastest 18 year-olds ever and the future looks bright for middle distance running in Great Britain.
Chirnside's Patrick Swan was also in superb form. Using the U23 Championships as a warm-up for the coming weekend's competition, 400m specialist Swan competed in the 200 metres, finishing fourth in the final after setting a new 200m personal best of 21.32.
Learmonth and Swan now go on to run in this weekend's senior UK Championships and European trials in Birmingham, which is televised on national TV.