Even if I knew for sure that I would live until age 85, I would not defer taking my state pension.
By deferring by one year, I might be better off from age 79 – but I don’t know many 79 year olds where extra money would make any applicable difference to their lifestyle.
On the other hand, if you are earning over £42K a year and draw your state pension, this extra pension money will be taxed at 40%. Assuming that once retired, your income does not reach your tax allowance, by deferring your state pension by 1 year, you will be better off after less than 6 years.
Even if you end up considering that you will pay 20% on your state pension (once drawn), which is likely if you have other pension income – then you will be better off in just over 7 years.