25% Tax Free in US IRA pension withdrawal?

I worked in the US for 25 years, I returned to the UK permanently in 2018 and I'm now planning retirement. My pension savings accrued while I was there are now in an IRA, still in the US. When I make withdrawals from that, will I be able to take 25% tax-free as I could with a UK pension? If the answer is yes, will the IRS respect that policy, or will they expect me to pay tax over there as it was not taxed in the UK? Thanks, Colin

Hi,
No, the full amount is taxable in the UK.
Thank you