The Citizens Advice service is one of the largest volunteer organisations in the United Kingdom with 21,600 volunteers. The majority of these are part-time volunteer advisers, but the figure also includes trustees and administrators. While volunteers have varying levels of training, they are all required to receive basic training to ensure they fully understand the nature of the service including the four basic principles. Typically there will be a paid bureau manager, advice session supervisors and in some cases some paid advisers. Some staff may be qualified to give specialist legal advice or to advise on immigration. Each Citizens Advice is an affiliated to the national organisation but they are managed and run locally. Many bureaux are also limited companies and may have a board of directors, who will also be the organisation's trustees. Bureaux throughout the United Kingdom have varying community needs and very different resources, and consequently offer different styles and levels of service. All bureaux in England, Wales and Northern Ireland are members of Citizens Advice, the operating name of The National Association of Citizens Advice Bureaux. Northern Ireland bureaux are also members of the Northern Ireland Association of Citizens Advice Bureaux (NIACAB). Bureaux in Scotland are members of Citizens Advice Scotland (CAS), part of the Scottish Association of Citizens Advice Bureaux. Citizens Advice holds an Annual Conference each year. In 2015 this was held at the University of Warwick.