A spokesman for Scotland Yard said: "All seven have had their bail extended to a date in November. The exact date is yet to be determined pending advice from the Crown Prosecution Service."
Gallagher arrived to answer bail at Charing Cross police station at 11.08am yesterday morning, almost 10 months after he and two other jockeys, Leighton Aspell and Jamie Osborne, were arrested and bailed in connection with the investigation.
Aspell was told earlier this year that no further action would be taken against him, while Osborne was released from bail on Monday. A file on his case has been sent to the Crown Prosecution Service, but Osborne said on Monday night that he was "confident" that he would be cleared in the near future.
The six others who attended Charing Cross police station to answer questions yesterday were: Brian Wright, Jason Moore, Ray Butler, Glen Gill, Adam Hodgson and John Mathews.
Wright, a former hotelier from Newmarket, arrived with his head completely wrapped in a scarf and a large hat pulled down over his forehead - confounding waiting photographers.
The men arrived at hourly intervals but, with each being questioned in turn by detectives, the schedule soon started to unravel.
Gallagher's solicitor Douglas Fordham, said yesterday evening: "Dean has been in the police station since approximately 11 o'clock this morning. He has been interviewed - he has not been charged - and there are a number of people the police are interviewing today.
"They are waiting until they have interviewed all those people until they make a decision as to what they are doing further."
Paul Raxstraw, representing Wright and Mathews, said shortly prior to the Yard's anouncement that bail was being extended: "They are still interviewing other people. They have told me they have someone else to interview and I think Mr Hodgson is last in the queue and once that is done they will have a de-briefing and make a decision."
The evidence in the case, which was initiated by the Jockey Club, is thought to date back to February 1997, a month before two horses, Avanti Express and Lively Knight, were doped at Exeter and Plumpton respectively.
The scope of the inquiry was widened when the cases of doping were confirmed. Aspell was the rider of Lively Knight, while Osborne was aboard Avanti Express. Both started as hot favourites for their races, and finished well beaten.
Allegations of possible race-fixing are, if anything, of even greater concern to the sport than doping. When a favourite is doped and runs poorly, the local stewards are almost certain to order a post-race dope-test, and the deception will just as inevitably be discovered.
If a race was fixed by one or more jockeys, one obvious way to make money would be to ensure a well-fancied horse wins with the conspirators' money riding on it. Since the result will have been widely expected anyway, an investigation is far less likely to result, and the deception will also be extremely difficult to prove. Suspicions of race-fixing are thus much more likely to shake punters' faith in the fairness of racing than isolated instances of doping.
The investigation which is in progress is by far the most detailed to do with racing in which the police have become involved.