The 29-year-old world No 27 should still be pleased with his performance at the Cumberland Lawn Tennis & Squash Club, however, given it is only four months since he underwent hip surgery.
Top seed Boswell – former world No 4 – had reached the final without dropping a game and continued that trend when he defeated second seed Kemp 11-3 12-10 11-5.
In the women's event Nottingham's Emma Beddoes outlasted compatriot Victoria Lust in the final to keep the title in English hands for the third year in a row.
Like Boswell in the men's event, Beddoes, reached the final without dropping a game, while fifth seed Lust made her breakthrough with a straight games victory over second seed Lauren Briggs in the quarter-finals.
But 25-year-old Beddoes, ranked 23 in the world, was too strong for her younger opponent, beating 21-year-old Lust 11-7, 12-10, 11-8 in 38 minutes to secure the fifth Tour title of her career.