Estimate could face a maximum of 18 rivals in defence of her Gold Cup crown at Royal Ascot.

The Sir Michael Stoute-trained five-year-old became the first horse in the 207-year history of the stayers' championship to carry the colours of a reigning monarch to victory when she won for the Queen last year.

However, the mare has an even taller order next week as she has not run yet this season.

A horse who will carry strong support on the home front is Brown Panther, bred and co-owned by former England striker Michael Owen.

The Tom Dascombe-trained six-year-old has been in the form of his life this season, chalking up convincing victories in Chester's Ormonde Stakes and the Henry II Stakes at Sandown in his two starts since his eighth in the Melbourne Cup.

Leading Light, winner of the Queen's Vase 12 months ago, heads the pre-post market.

Victorious in the Ladbrokes St Leger in September, Aidan O'Brien's charge has already demonstrated his well-being this term with victory in the Vintage Crop Stakes at Navan.

O'Brien also has El Salvador, Ernest Hemingway and Eye Of The Storm, while other Irish-trained possibles are Simenon, last year's runner-up for Willie Mullins, Royal Diamond, Saddler's Rock, Ralston Road, Missunited and Pale Mimosa.

Marco Botti has left in Tac De Boistron, winner of the Prix Royal-Oak and Sagaro Stakes, while Godolphin rely on Ahzeemah, trained by Saeed bin Suroor.

German raider Altano could try to improve on his fifth place in the race last year for trainer Andreas Wohler.

Completing the list of six-day confirmations are Oriental Fox, Whiplash Willie, Havana Beat and Shwaiman.