By Ben Cleminson NO BRITISH-trained horse has ever won the Group One Chairman’s Sprint Prize (Sunday, 7.50am), but that isn’t stopping trainer George Boughey and owners Highclere having a crack at the £2.2 million pot with four-year-old filly Believing. The daughter of Mehmas finished a close third in the Haydock Sprint Cup last September following a Group Three success at Chantilly earlier in the season. Boughey has had great success since saddling his first runner in 2019, culminating in Cachet landing the 1000 Guineas in 2022, also for Highclere. France has been a happy hunting ground for t…