Lump sum backdated pay ruses

Hi, I'm currently earning £50k+ and stand to receive in excess of £13k gross representing two and a bit years of backdated pay rises. We're awaiting clarification as to whether this will be paid in one (4-weekly) salary instalment, or (as is more likely) paid in unequal instalments over three salary instalments. What are the implications of both scenarios? If I understand correctly it's largely immaterial as to when or how it's paid during the tax year in terms of overall tax liability, but, if its paid over three instalments presumably it will take longer for my 4-weekly PAYE to return to 'normal'? So, assuming the lump sum is spread over Oct, Nov, Dec, should the tax paid be significantly lower for Jan, Feb, Mar to balance the tax by the time the P60 is calculated? .....and is it actually likely to happen in this way dynamically through PAYE or more likely (due to dragging things out over three months) that a refund of overpaid tax is carried over to the next financial year?

Hi,
After the 3 extra payments have been made, your pay should revert to what it was before and the tax deducted each month should be the same as before.  
A cumulative tax code calculates the tax payable on your earning to date and the tax you pay is the difference between this calculation and the tax to date for the previous month.
Thank you.