NHS Pension Scheme Pays

Edale

I am looking at pension contributions in excess of the annual allowance of around £28,000 this year (even taking into account carry forward) and am trying to work out if it is best just to pay the tax on this or to use scheme pays. My understanding of how the annual allowance charge and how the scheme pays works is as follows, please let me know if I am wrong in any way or if I have missed anything.

If I just pay the tax, then £28,000 will be added to my income and as an additional rate taxpayer I will have to pay additional tax of 45%x £28,000 = £12,600 from income already taxed, is that correct?

If I elect for scheme pays, then I have to choose one of the schemes I am a member of (ie 2015 or 1995) to take all of this year's charge, Is the amount then used the £28,000 or the tax on it ie £12,600?

Assuming, as I believe, it is just the tax due then the £12,600 sits as an effective loan until I take the pension accruing annual interest at the SCAPE rate, currently 1.7% + September CPI.

On retirement the £12,600 plus interest is divided by a factor to give a deduction from the final pension. The factor depends on age and as an example would be 25.8 in the 1995 scheme if retiring at 56, meaning the annual pension would be reduced by £12,600/25.8 (plus interest) or £488.37 and the lump sum reduced by 3X £488.37= £1465.11. 

If the above is correct and as I am going to be a higher rate tax payer in retirement, it looks like it is a no-brainer to do scheme pays rather than paying out of savings as I am losing £488.37-40% = £293.02 per annum plus £1465.11 tax free lump sum but keep £12,600 in my bank.

The only other question is if I am best doing it from the 1995 scheme of the 2015 scheme, as a higher rate taxpayer in retirement, I assume the tax free lump sum as standard in the 1995 scheme is more valuable and hence I am better using the 2015 scheme with even though it has a higher reduction in pension (factor is 22.8 rather than 25.8 as above so pension reduced by £552.63 rather than £488.37 plus lump sum reduction of £1465.11)