//Implementation of IFiltrable
 public bool FilterClause(string filter)
 {
     return(City.ToLower().Contains(filter) ||
            CountryName.ToLower().Contains(filter) ||
            Forename.ToLower().Contains(filter) ||
            PersonTypeName.ToLower().Contains(filter) ||
            Postcode.ToLower().Contains(filter) ||
            Surname.ToLower().Contains(filter));
 }