honest taxpayer

I have a pension that I invested in prior to becoming tax resident in the UK. The pension was invested in 1994 - 2008 in foreign country. I became a tax resident in the UK in 2008. I would like to withdraw the pension from foreign country and bring to the UK in the 2024/25 tax year. Will all of this be taxed or only the portion since becoming tax resident in the UK i.e. 16/30 years portion taxed in the UK with 14/30 not liable to UK tax?