//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));
}