Roth IRA Withdrawal for non-US Expat in UK

Hello, I am seeking advice on the UK tax implications regarding a Roth IRA I hold in the United States. I originally contributed to this Roth IRA while living in the US, and the account value has since grown from $16,000 to $20,000. I am no longer a US resident as I have relinquished my green card. Could someone please clarify: How will the UK tax authorities view the withdrawal of these funds? Are there any specific reporting requirements I need to follow upon withdrawing and transferring these funds to the UK? Will the growth portion ($4,000) be subject to UK taxation, and if so, how is this calculated? I would appreciate any guidance or resources that can assist with this query. Thank you.

Hi,

Roth Individual Retirement Accounts payments to a UK resident that are not taxable in the United States are not taxable in the United Kingdom. Guidance in relation to other pensions can be seen at Note 2 in the following guidance:

DT19852 - Double Taxation Relief Manual: Guidance by country: United States of America: Treaty summary

Thank you.

Thanks, and what happens if they're taxable in the US?

Hi foobsall,
Roth IRA schemes are not taxable in the USA, so are not taxable in the UK.
Thank you.

Hi, my custodian said that due to my non-resident alien status, they will apply 30% NRA withholding tax to any withdrawals made. Can you please confirm if this is correct? I believe US/UK DTA stipulates that the withholding may not be necessary where there is a treaty https://www.irs.gov/publications/p515, and the US/UK DTA treaty states only the UK can tax my withdrawal https://www.gov.uk/hmrc-internal-manuals/double-taxation-relief/dt19852 (as you mentioned). I'd like to not have this 30% applied or, at least, figure out how to get it back.

Hi, foobsall,
Article 17(2) of the UK/USA DTA provides the US with the right to tax any Lump Sum payment which is made from a US sourced pension scheme (including IRAs).
However, the UK is also permitted to tax the same lump sum payment(s), which is in accordance with Article 1(4) of the DTA – Both Article 17(2) and Article 1(4) are outlined below and, when read from the perspective of a UK resident, state: 
Article 17(2) - Notwithstanding the provisions of paragraph 1 of this Article, a lump-sum payment derived from a pension scheme established in a Contracting State [USA]and beneficially owned by a resident of the other Contracting State [UK]shall be taxable only in the first-mentioned State [USA]. 
Article 1(4) - Notwithstanding any provision of this Convention except paragraph 5 of this Article, a Contracting State [UK and/or USA]may tax its residents, and by reason of citizenship may tax its citizens, as if this Convention had not come into effect.   
A UK resident, Article 1(4) above permits the UK to tax any US sourced Lump Sum payment received, as if Article 17(2) of the DTA was not in force or applicable – Article 1(4) effectively ‘overrides’ the provision at Article 17(2), and the consequence is that both the UK and USA can tax any Lump Sum payment received from a US sourced pension scheme. 
In these situations, double taxation will occur since both the UK and the USA can tax the same income. However, that double taxation will be eliminated in accordance with Article 24(4)(a) of the DTA which requires the UK (as the country of residence) to provide FTCR to offset the US tax correctly paid against the UK tax charged on the same the IRA withdrawal.  
Thank you.