Analysis of Each Runner:

1. Alexandroupolis: Sired by a St Leger runner-up and a relative of another St Leger winner, his pedigree suggests he’s cut out for this sort of test. However, his recent form is mixed. While he showed promise in a Galway maiden, his subsequent runs were not as impressive. His last outing had him checked and trying to recover from a disadvantaged position. While he remains unexposed, he does not bring any strong form claims into this contest.
2. Arrest: Boasts solid form, particularly on softer grounds. His victories in the Chester Vase and the Group 3 at Newbury are notable. He’s shown his preference for ground with a bit of give, which he should get here. His stamina is not in question, and he carries some of the best form into this race.
3. Chesspiece: Has been progressing well, showing a steady improvement in form. His third-place finish at the Queen’s Vase and victory at Hamilton indicate potential. While there are others with better form, the step up in trip might play to his strengths.
4. Continuous: This horse’s form is impressive. His win in the Great Voltigeur at York is significant, and he seems to be a horse on the rise. He is already showcasing some of the best form in the field and seems versatile in terms of ground and distance.
5. Denmark: Has shown he can handle very soft ground, but his recent performances leave some doubts. He has tendencies to hang and can be hard to settle, which can be detrimental in a race of this caliber.
6. Desert Hero: Has been steadily improving, showcased notably with his Royal Ascot and Goodwood victories. While the step up in distance raises questions, his recent form suggests he is still on an upward trajectory.
7. Gregory: Has strong form lines, particularly his win at the Queen’s Vase. The shift back to this distance might just be what he needs to excel. However, the departure of Dettori to ride another entrant may raise eyebrows.
8. Middle Earth: Demonstrates potential, having a recent win at Newmarket and showing prowess in the Melrose Handicap. Moving into his first Group race, he has a lot of promise.
9. Tower Of London: His form has significantly improved over middle distances. With victories at Leopardstown and Down Royal and being a sibling to a Leger winner, he brings strong credentials into the race.

Summary:
Based on form, ground preference, and progression, the strongest contenders appear to be Arrest, Continuous, and Gregory. Arrest and Continuous have shown consistent form, especially on softer grounds, which is expected for this race. Gregory is well-bred for this contest and will relish the step up in distance.

Conclusion:
In the St Leger stakes, it would be wise to keep an eye on Arrest and Continuous due to their proven form on soft grounds and notable recent performances. Gregory could be a danger, given his breeding and potential to thrive at this distance. One for each way backers could be MIDDLE EARTH. He’s shown noticeable improvement in a short span of time and his recent performances indicate untapped potential. His victory in the Melrose Handicap suggests that he’s a 3-year-old stayer on the rise, and he might just deliver a surprise against more fancied rivals. While he might not be the most obvious choice based on some of the higher-profile form in the race, his trajectory and the potential for further improvement make him an intriguing contender.