Federal tax in the US

I worked in the US for 6 year and I put money into a cash IRA account it’s like an isa over here. When I tried to bring it back into this country they told me I would withhold 40% for federal tax. Can I claim this back.

Hi,
Payments made by the individual into an IRA, are made after tax relief is given to the individual by the employer. Payments from this pension are taxable in the USA.  
HMRC does not recognise IRA schemes as pensions, so for UK residents, they are taxed as income under the interest banner and declared as foreign interest on a tax return (SA106).  
There is no US taxation if the pension is subject and liable to UK tax. If US tax is withheld, then the individual,  should seek a refund of this tax (file a form 1040NR).  
HMRC will not give a credit for this tax against any UK tax charged on this income.
Thank you.