Pensions and tax relief

I have two linked questions regarding this year's changes in tax relief on pension contributions. Does the limit on contributions of £20,000 for the next two years apply even though my current income is below £150,000 and is not likely ever to exceed it as I have gone half time? Does the limit also apply to lump sum contributions for additional pension within the NHS Pension Scheme? NHS Pensions' calculator at www.nhsbsa.nhs.uk/pensions tells me that purchasing £5,000 worth of extra pension a year will cost £90,400. Although I cannot afford this much I would like to put in an amount equivalent to my income paid at the tax band of 40 per rate in the year in which I retire.