The Kawasaki rider, who has started from the front of the grid at seven of the nine rounds so far, set a time of 2mins 6.115secs on a track that was drying after morning rain.
That lap from the Huddersfield rider ensured that he and second placed Carlos Checa were the only title contenders to end the day inside the top ten.
Championship leader Max Biaggi languished in 17th for Aprilia, with BMW’s Marco Melandri and Leon Haslam 12th and 13th.
Honda’s Jonathan Rea 18th, fresh from victory at the Suzuka Eight Hours last weekend, was even worse off down in 18th spot.
Biaggi and Rea will be hoping that rain does not materialise ahead of today’s second qualifying session or they face missing out on a place in Superpole.
Reigning world champion Checa, a double winner at the Northamptonshire track last year, ended the session just three hundredths of a second off Sykes’ pace, having led the way in the morning’s free practice.
Behind Checa, French rider Sylvain Guintoli made a sensational debut for the PATA Ducati team by setting the third fastest time ahead of the British pair of Leon Camier and Chaz Davies, who produced strong performances for Fixi Crescent Suzuki and ParkinGO MTC Aprilia respectively.
Jakub Smrz was sixth ahead of Eugene Laverty, with the unlikely figures of Lorenzo Zanetti, Maxime Berger and John Hopkins rounding out the top ten.