THE 215th Derby at Epsom this afternoon is widely recognised to be one of the most open and a race which is unlikely to contain a true champion. But if the Classic is to be contested by forgettable horses it may well become legend as the last hurrah for the greatest jockey the Derby has seen, Lester Piggott.

Forty years after his first victory in the race, on Never Say Die, Piggott takes his 36th Derby ride on the 25-1 shot Khamaseen amid speculation that this will be his last ride in the race. William Hill, the bookmakers, have put statistics to the suggestion and go

11-10 that the 'Long Fellow' will not ride in next year's race. Today may be the last chance to see the man who partnered Sir Ivor, Nijinksy and The Minstrel to success in the world's most celebrated Flat race.

''Lester is 58 now and has ridden nine Derby winners, but he has ridden only a handful of winners (one in Britain) of any description this year and some racing experts are beginning to write him off,' Graham Sharpe, Hills' spokesman, said yesterday. 'But we just reckon he will be back next season and it wouldn't be long odds that eventually he'll become the first pensioner to win the race.'

While Piggott's prospects this year may be slim, the Derby may still go to a grandfather. The favourite, Erhaab, is to be ridden by 51-year-old Willie Carson, who has been chasing Piggott for much of his career and who will now beat him into the record books as the third oldest man to win the race if he succeeds today on his 26th attempt.

Erhaab has been well backed (especially as the ground has dried up to the present good going) for a particularly well- contested Derby - the field of 25 is the largest since Shirley Heights led home a similar number 16 years ago - but he is not the biggest loser for Hills. That position belongs to Broadway Flyer, the second favourite. The result that would please those bookmakers most would be succees for The Flying Phantom, who is the worst backed horse in the history of the race. While money has been flying across the counter for others in the race, the 250-1 shot has been almost totally ignored. So far, Hills report bets on him totalling pounds 6.