Davidson's mount, 13-year-old Squelch, won the three-day event at Blenheim in 1994. Gifford's State Diplomat also has a three-day event victory behind him, having won at Le Lion d'Angers in France in 1996 before he knocked a tendon and had last year off.
"He's an attractive horse and he moves very well," Gifford said of State Diplomat, who plodded round in deep mud at Bramham this year to finish 21st. "We went towards the end of the day when the mud was at its worst, so there was no need for heroics."
Thompson, lying one point ahead of the 1997 Bramham winners, Australia's Andrew Hoy and Swizzle In, had her usual good test on Welton Romance apart from a ragged rein-back. She expects to ride Romance at Burghley next month, retaining the mare's half-brother, Welton Molecule, for the World Equestrian Games in Italy in October.
At 48, Davidson shows no signs of taking things easy. He rode four horses in the dressage yesterday and will take all of them in the show jumping and cross-country today. Gifford is riding two dressages as well as show jumping and cross-country phases with four horses.
Owen Moore, who - like Gifford - is on the British short-list for the World Games, took an early lead for the Intermediate Championship on the seven-year-old Lord Killinghurst.
DOUBLEPRINT BRITISH HORSE TRIALS CHAMPIONSHIPS (Gatcome Park) Standings after first half of dressage: Advanced Section 1: 1 Squelch (B Davidson, US) 23 penalties; 2 State Diplomat (K Gifford, GB) 24; 3 Welton Romance (L Thompson, Irl) 26. British Intermediate Championship: 1 Lord Killinghurst (O Moore, GB) 26; 2 Voyou du Roc (M Fuse, Japan) 28; 3 Zambesi Spirit (E Watson, GB) 29.Reuse content