Upon the motion of any party made after a verdict has been  returned and before the jury has dispersed, the jury must be polled. The judge may also upon his own motion require the polling of the jury. The poll may be conducted by the judge or by the clerk by asking each juror individually whether the verdict announced is his verdict. If upon the poll there is not unanimous concurrence, the jury must be directed to retire for further deliberations. (1977, c. 711, s. 1.)