Parish councillors remain parish councillors until 4 days after the elections (ss 16(3) & as 35 (2) LGA1972. The exception is the chairman and vice chairman who retain their office until the May meeting. - At this point the chairman and vice chairman remains their postion even if he was not reelected, and until their successor is appointed.
ALL councillors take office on the 4th day after elections, but may make their declaration as soon as they are elected (e.g. without contest)
Reelected councillors must still make their declaration in then same way as new members.