Your salary spans the Basic Rate (20%) and Higher Rate (40%) bands. You pay 20% on income between £12,570 and £50,270, and 40% on income between £50,270 and £70,000.
Your estimated Income Tax on £70,000 is £15,432, giving you an effective Income Tax rate of 22.0%. Combined with National Insurance of £3,411, your total deductions are £18,843, or 26.9% of your gross salary.
Since your salary exceeds £50,270, the portion above this amount is taxed at the Higher Rate of 40%. National Insurance also drops from 8% to 2% above this threshold, providing a small offset.