Naturalisation - referees

[Leo54]

My partner will be eligible to apply for naturalisation in Summer 2009. We are aware that he needs two referees, one of whom must be a person of 'professional' standing, and that both must have known him for at least three years.
Does anyone have a full list of the people allowed by the Home Office in the 'professional' category?
For both referees, does anyone have details of the type of information they will be asked to provide in support of the application (over and above the basic information on the application form). Are they sent a questionnaire by the Home Office, or do they have to write a detailed letter supporting the application, or are they interviewd, etc., etc. I'm assuming it is more than their just confirming that they know the applicant.
Any details much appreciated. Thanks.

[John]

Leo, exactly this same subject has come up before. For example have a look at this topic (click).

To avoid duplication I shall now close this.