All his income will be added together including any pension he draws. He can then claim some expenses to reduce the income figure, but for most PAYE people these claims will be zero. There is one very important claim he can make and that is contributions to a personal pension. That last sentence is going to be VERY VERY important for his decision on drawing his state pension.
All income below £12570 is tax free, the next £37700 is taxed at 20%, the total tax in this band is £7540 anything above £50270 is taxed at 40%.
By deferring his state pension by one year it will be increased by the government by 5.8% for the rest of his life. For simplicity I will assume the state pension is £10k per year. By deferring 1 year he will lose £10k, but there after he will get £580 per year extra. It will take him just over 17 year to make up the £10k he lost out on. So he needs to live to beyond 85 to make deferring make sense.
The actual state pension will be about £15k by the time he retires, but that has no effect on the 17 year pay back period.
Here is what I would do in this situation. Draw the full state pension as soon as possible, keep on working as long as he is happy doing that, make a MASSIVE contribution to the private pension every year, to get below 40% tax (as long as you can both live comfortably on the £50k that is left). To all intents and purposes he is drawing his state pension to pay into his private pension tax free. You (and he) will then be able to draw on a much bigger pot when you want to. He needs to get as much money out of the government pension as soon as possible and get that money into his personal pension, which he (and you) can control.
The budget may effect the rules about pension inheritance and tax reliefs, but under the current system, what I am suggesting will improve your retirement finances a lot.
I'm not a tax advisor, but I know how to plan my affairs tax efficiently.