He followed up an impressive win in the 200 metres freestyle by finishing four seconds clear of the field in the 400m in 3min 53.71sec.
Palmer, who pulled out of the Commonwealth Games last year due to fatigue, said: "I have never done these times when I haven't shaved down or tapered so it's looking good."
On Saturday, Sue Rolph lowered her long course 50m freestyle record by 0.03sec to 25.54. "I could not believe the time. I've had three weeks of back-to-back training sessions. I did not think I would go under 26 seconds," she said.
Two British junior records fell. Matthew O'Brien, 16, lowered his own 100m backstroke record to 58.99sec in the heat and again in the final to 58.26. He finished fourth. Nicola Jackson smashed the British junior long course 100m butterfly record for the second time in a week. She clocked 1min 2.05sec was half a second faster than the time she set in Vancouver a few days earlier and 0.7 faster than the previous junior mark, set 21 years ago by Ann Osgerby.
Franziska van Almsick, the world record holder, failed to qualify for the 200m freestyle of the European championships with a disappointing performance at the German nationals this weekend. Van Almsick missed the final after swimming a modest 2min 4.75sec in her heat on Saturday in Leipzig. Kerstin Kielgass won the title in 2:01.38.