Underwood had a great competition, winning both the girls’ B one-metre and three-metre springboard titles.
She took victory in a highly-competitive one-metre competition by just two points from Albatross Diving Club’s Lauren Saunders.
But then claimed the three-metre British gold medal by more than 14 points, with Saunders taking silver again.
Great Britain junior star McCabe also returned home with two medals.
He won silver in the boys’ A platform event on the final day of the championships. He and Southampton’s Robbie Lee had a great battle for gold. The pair were well ahead of the rest of the field and McCabe finished with a stunning 83.30 points for his reverse three-and-a-half somersault tuck dive.
McCabe also took bronze in the three-metre springboard event behind London’s Hugo Thomas and Leon Baker.
Fellow Plymouth divers Ollie Heath, Theo Stevens, Archie Waines, Katie Martin and Scarlett Colbourne also qualified and competed at the championships.
Heath just missed out on a place in the final of the boys’ B platform competition, finishing seventh in the prelims. Team-mate Waines was 11th in the same event.
In the boys’ B three-metre category, Heath came 10th, Stevens 15th and Waines 17th, while in the one-metre, Stevens was seventh, Heath 13th and Waines 15th.
Stevens and Heath also teamed up in the boys’ three-metre synchro event for 14-18 year-olds and came sixth.
Martin and Colbourne were also sixth in the girls’ three-metre 14-18 years’ synchro competition.
Martin came 10th in the girls’ A three-metre prelims and 13th in the one-metre competition.
Colbourne finished eighth in the prelims of the girls’ B three-metre event and was also ninth in the platform prelims.