Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
Contributions to a pension scheme are allowable against Income Tax in the computation although the limits are being squeezed. You should declare your full income and the sacrifice as a pension contribution. This should reduce your income hopefully to a level below the higher tax bracket.
Remember that pension contributions in the 15/16 tax year may not exceed 40K and your overall pension pot (lifetime allowance) 1.25 million quid. In 16/17 this drops to 1m.
I do hope that you have found my reply of assistance.
Thank you for your support.