Simler J, sitting in the Employment Appeal Tribunal has held that an employee who gave seven months notice, when only required to give three affirmed the contract and was therefore unable to claim constructive dismissal.
The essential reasoning of the Judgment is that there must come a point whereby notice in excess of the notice period amounts to affirmation. However, it does not follow that in every case where notice is in excess of the minimum, affirmation will have occurred. As to what amounts to affirmation is a question of fact.
A copy of the Judgment (Cockram v Air Products) is here: http://www.bailii.org/uk/cases/UKEAT/2014/0038_14_2105.html