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The only things that could reduce your income tax liability if you got married would be the married couple's allowance or the marriage allowance which you can read about here and here respectively.
For the married couple's allowance, one or both of you needs to have been born before 6 April 1935. The marriage allowance is available to those couples where both spouses were born after 5 April 1935.
I hope this helps but let me know if you have any further questions.