Dual Citizen Investing: A UK Investment Case Study

For UK residents who are also US citizens, finding suitable investment solutions can be more complicated than it first appears. Some banks and investment platforms do not support US citizens, leaving people with fewer options and, in some cases, no clear investment strategy at all.

This case study looks at how Castle Stonebridge supported a UK/US dual citizen who had been declined by banks because of her citizenship status. She had accumulated substantial cash from surplus income, with the interest on those savings being taxed at 40% because of her income tax position.

The client was unaware that a suitable investment strategy could be available to her. Through a tailored approach to UK resident dual citizenship clients, we were able to consider her short, medium and long term objectives, manage investment risk and make better use of available UK tax allowances.

The client's starting position

The client had a strong income and had built up significant cash reserves over time. Rather than being invested across a wider portfolio, much of her surplus money had remained in cash.

This was partly because she had previously approached banks about investment products and had been declined due to her US citizenship. Like many people in a similar position, she had assumed that investing through a UK financial provider might simply not be possible.

The result was a large amount of money sitting in cash without a wider investment strategy behind it.

There was also a tax consideration. As a higher rate taxpayer, the client was paying 40% Income Tax on savings interest above her available allowance. For 2026/27, the Personal Savings Allowance for a higher rate taxpayer is £500. (GOV.UK: tax on savings interest)

40% higher rate Income Tax

The client's savings interest was creating an ongoing tax liability of £7,634 because of her income tax position and savings held.

The challenge with US citizen investing

The first challenge was finding an investment solution that could accommodate the client's circumstances.

Some UK investment platforms and financial providers do not accept US citizens because of the additional regulatory and tax considerations associated with US citizenship. This can make finding appropriate dual citizen investing solutions considerably more difficult.

In this case, the client had already experienced that problem first hand.

The objective was therefore not simply to recommend an investment portfolio. We first needed to establish what financial products and services were available and suitable for someone with her citizenship status.

Once this had been established, we could look at how her money could be structured around her objectives.

Moving from cash to a structured investment strategy

The client did not need all of her money to be held in cash.

Cash remained important for short term requirements and accessible reserves, but holding everything in cash meant that the longer term portion of her wealth had limited opportunity for investment growth.

Inflation can also reduce the real spending power of cash over time. Even where savings earn interest, the return needs to be considered alongside the rising cost of goods and services.

The new US citizen investing strategy therefore divided the client's financial objectives by timeframe.

The portfolio was structured around the client's attitude to investment risk and her financial objectives rather than simply moving as much money as possible out of cash.

Making better use of available allowances

Tax planning was another important part of the review.

The client had previously been unable to make use of some UK investment allowances through the solutions available to her. The new strategy created opportunities to consider allowances such as ISAs and the Capital Gains Tax annual exempt amount.

For the 2026/27 tax year, the overall ISA allowance is £20,000. Investments held within an ISA are exempt from UK Income Tax and Capital Gains Tax. (GOV.UK: how ISAs work)

The Capital Gains Tax annual exempt amount is £3,000 for individuals in 2026/27. (GOV.UK: Capital Gains Tax allowances)

2026/27 allowances

£20,000 overall ISA allowance
£3,000 Capital Gains Tax annual exempt amount
£500 Personal Savings Allowance for higher rate taxpayers

The important point was not simply to use every allowance available. The allowances needed to fit within an investment strategy that made sense for the client's objectives and circumstances.

For dual citizen investing, there is also an important additional consideration: UK tax treatment does not necessarily tell the whole story.

US citizens can remain subject to US tax and reporting requirements even when living in the UK. The UK and US have a double taxation agreement, but the interaction between the two tax systems can be complex. (GOV.UK: USA tax treaties)

For that reason, clients in this position may also need specialist US tax advice alongside UK financial planning.

How could the client take income in the future?

Another objective was to establish a clearer strategy for future withdrawals.

Rather than simply allowing savings interest to accumulate and then withdrawing money when required, the client's investments could be managed with future income requirements in mind.

This meant considering which investments and tax wrappers could be used for different purposes and how withdrawals could be structured as part of the wider financial plan.

The aim was to give the client greater control over when and how she accessed her money, while considering the tax consequences of different approaches.

For dual citizen investing, this is particularly important because the most tax efficient approach from a UK perspective may require further consideration from a US tax perspective.

High intent questions about dual citizen investing

Can a US citizen living in the UK invest through a UK financial adviser?

Yes, suitable investment solutions can be available, although some UK providers and platforms have restrictions on US citizens. The available options need to be assessed based on the individual's circumstances.

Can US citizens have an ISA?

A UK resident can generally qualify for an ISA if they meet the UK residence requirements. However, US citizens should not assume that an ISA receives identical tax treatment in the US. The US tax position should be considered separately.

Why were the client's savings being taxed at 40%?

The client was a higher rate taxpayer. Higher rate taxpayers generally have a £500 Personal Savings Allowance, with savings interest above the relevant allowance potentially subject to Income Tax. (GOV.UK: tax on savings interest)

Is investing better than keeping money in cash?

Not necessarily. Cash can be appropriate for emergencies and short term spending. Investments are generally more suited to money that can remain invested for longer and where the investor accepts the possibility of losses in exchange for potential growth.

The outcome for the client

The biggest change was that the client no longer had to assume her US citizenship prevented her from having a suitable investment strategy.

Through tailored dual citizen investing advice, her finances could be structured around different time horizons, with appropriate cash reserves alongside a diversified investment portfolio aimed at long term growth.

She could also consider UK tax allowances that had previously been difficult to access, while establishing a clearer strategy for future income withdrawals.

The result was a financial plan designed around the client's circumstances rather than the limitations she had experienced when approaching mainstream banks.

How Castle Stonebridge can help

This case demonstrates why US citizen investing can require a more tailored approach than a standard UK investment strategy.

At Independent Financial Advisers | Castle Stonebridge Financial Planning, we can review your existing savings and investments, understand your objectives and consider how investment, risk and tax planning could work together.

For clients with dual citizenship, the first step is understanding what is actually available and how it fits into the wider financial plan. Where US tax considerations apply, specialist US tax advice may also be appropriate.

The key takeaway

This client's experience shows that being a UK/US dual citizen does not necessarily mean you have to leave your savings sitting in cash simply because mainstream providers have declined to help.

The right US citizen investing strategy needs to take account of investment risk, tax allowances, future income requirements and the additional considerations created by US citizenship.

For this client, the result was a move from an unnecessarily cash heavy position towards a structured investment strategy designed around her short, medium and long term objectives.

*Disclaimer: The value of investments and the income they produce can fall as well as rise. You may get back less than you invested. The benefits to the treatment of tax will depend on your individual circumstances and may be subject to change in future. This is one example and outcomes will vary depending on circumstances.