Abel Haddon, who gave advice informally to Prince Edward in the mid-1990s, is said to be favourite for the high-profile post.
The appointment of a new spokesman has been presented as an important symbol of the modernisation of the monarchy following the death of Princess Diana last year.
Mr Haddon has had a long career in PR working for Sir Tim's firm, Lowe Bell, which held the accounts of several prominent figures including Andrew Lloyd Webber. More recently he has worked for Edelman PR agency.
Other contenders include Howell James, former political secretary to John Major, and Charles Anson, who held the job of press spokesman at the Palace before joining the private sector.
Mr James is thought to be an unlikely choice in view of Mr Major's poor publicity, and the fact that the appointment of someone linked so closely to a political party would be controversial.
The appointment of Mr Anson, who enjoyed good relations with the Queen, would be interpreted as a return to the Palace's old ways.
Although Mr Haddon worked for Lady Thatcher for six months, he did so after she left office in 1990 and is not seen primarily as a political practitioner.
Mr Haddon said last week that he has had no discussions about the job but declined to rule himself out. Asked if he was interested, he replied that the question was "hypothetical".
Recruitment for the job, which is expected to pay a six-figure sum, is being handled by a headhunter. It is thought that names are being debated before any approach is made.Reuse content