If you just consider your earnings of £30k and take none of your pension pot you will see deductions of £3,880 income tax and £2,632 National Insurance, a total of £6,512 .
Looking now at the pension pot, you can take your £25k tax free leaving you with £75k to worry about. If you took all of it and had it taxed as earnings in a single year you would have a taxable income of £105k for the year. Your personal tax free allowance will reduce by £2,500 to £8,100 (it reduces by £1 for every £2 you earn over £100k). You will therefore pay tax on £96,900. You will pay 20% on this income between £8,100 and £39,885 which is £6,357. You will pay 40% on the remaining £65,115 which is £26,046. So your total tax bill will be £32,403. However there is also National Insurance to consider. The NI threshold kicks in at £8,060. You pay 12% between this lower threshold and £42,380 which is £4,118. You then pay 2% on your remaining £62,620 which is £1,252 making your total NI bill £5,370. So your total deductions for the year will be £37,773.
In taking the extra £75k you will see additional deductions of £31,261 (41%). This means you will be left with just £43,739.
To minimise this extra tax burden you need to keep the amount you draw to below the higher rate income tax threshold. For next financial year this is £42,385, meaning you can take £12k or so. You would then lose “only” 32% of any amount you draw (20% income tax and 12% National Insurance).