How to claim tax treaty protection for IRA?

A previous thread mentioned that if you are a US citizen, UK resident, and have an IRA, you need to file a UK tax return specifically requesting tax treaty protections be applied to your IRA. See http://talk.uk-yankee.com/index.php?topic=60995.msg865453#msg865453 (not resurrecting that thread due to its being over 1 year old)

My question is where on the UK tax return do you claim treaty benefits for an IRA? Also must you do it each year you hold the IRA, or only in the event you take a distribution?

Thanks!

So no one on the forum has an IRA?