Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
In my opinion this cannot be allowed as the actual payment was made in a later accounting period. Royal London advise:
'Remember, tax relief can only be given on contributions that have actually been paid'
However, it might be possible to approach the relevant tax office for advise as HMRC may be inclined to allow the charge against current year.
Remember that there is an annual limit on pension contributions, the combined total of own and employer's may not exceed 40K.
I do hope that you find my reply of assistance.