there is a tax treaty between the US and UK which likely makes your pension only taxable in one country. unless someone can provide further guidance seek professional help.
here is the treaty. pensions are discussed in Articles 17 and 18.
https://home.treasury.gov/system/files/131/Treaty-UK-7-24-2001.pdf
if it is taxable say only in the UK there will be no FTC available for US purposes.
