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The short answer
A UK ISA lets a UK resident aged 18 or over save or invest up to £20,000 in the 2026 to 2027 tax year with no UK tax on the interest or gains. Naira savings pay much higher headline rates (the 364-day Treasury bill cleared at 15.85% on 7 October 2026), but you carry the risk that the naira falls against the pound, and interest earned in Nigeria is generally taxable in the UK if you are UK resident. The right split depends on which currency you will spend the money in.
The question usually arrives as a comparison of two numbers: a UK cash ISA paying a few per cent, and a naira deposit or Treasury bill paying four or five times that. Comparing those numbers directly is the most common mistake. They are paid in different currencies, taxed differently and exposed to different inflation. This guide sets out how each works for a Nigerian living in the UK.
What a UK ISA gives you
An Individual Savings Account is a UK tax wrapper. GOV.UK states that in the 2026 to 2027 tax year the maximum you can save in ISAs is £20,000. The types are cash ISAs, stocks and shares ISAs, innovative finance ISAs and Lifetime ISAs. You must be 18 or over (and under 40 to open a Lifetime ISA), and you must be resident in the UK, apart from some Crown servants and armed forces members. ISAs cannot be held jointly.
Interest and gains inside an ISA are free of UK tax. Outside an ISA, most people still have a Personal Savings Allowance: £1,000 of interest a year for basic-rate taxpayers, £500 for higher-rate and nothing for additional-rate taxpayers, plus a starting rate for savings of up to £5,000 for people whose other income is under £17,570.
If you later leave the UK, GOV.UK says you can keep the ISA and its tax relief but cannot pay in while non-resident, and you must tell your provider. That matters for anyone planning to move back.
What naira savings give you
Naira rates are higher because Nigerian inflation and policy rates are higher. The CBN cut the Monetary Policy Rate from 26.5% to 23% on 22 September 2026. At the Treasury bill auction of 7 October 2026, stop rates were 15.50% for 91 days and 15.85% for 364 days. Bank fixed deposits are negotiated per bank and amount. Headline inflation was 14.63% in September 2026, according to the NBS.
The catch is currency. Your return in pounds depends on the naira rate when you convert back. If the naira weakens by more than the interest gap over the period, the higher rate is wiped out. For how Treasury bills are bought from Nigeria, see how to buy Treasury bills in Nigeria.
Tax: the part most comparisons leave out
GOV.UK explains that UK residents are normally taxed on all their income, wherever it arises, while non-residents pay UK tax only on UK income. So naira interest earned while you are UK resident is generally reportable to HMRC, converted to pounds. The 1987 UK-Nigeria double taxation agreement caps Nigerian tax on interest paid to a UK resident at 12.5% and provides credit for tax paid in the other country. GOV.UK also sets out reliefs that may apply to some people new to the UK, so check your position. This is information, not tax advice.
Side by side
| UK cash ISA | Naira savings or T-bills | |
|---|---|---|
| Currency | Pounds | Naira |
| UK tax on interest | None inside the ISA | Generally taxable if you are UK resident |
| Annual limit | £20,000 across ISAs (2026 to 2027) | No UK limit; bank or auction minimums apply |
| Deposit protection | FSCS up to £120,000 per person per firm | NDIC cover up to its applicable limit |
| Main risk | Rate below UK inflation | Naira falling against the pound |
| Who can open | UK residents aged 18+ | Depends on bank; BVN or NRBVN usually needed |
A worked example
This example uses round, made-up numbers to show the mechanism, not a forecast. You have £5,000. A UK cash ISA pays 4% a year. A naira deposit pays 16% a year. You convert at ₦2,000 per £1 today.
- ISA after one year: £5,000 × 1.04 = £5,200, with no UK tax.
- Naira after one year: ₦10,000,000 × 1.16 = ₦11,600,000 before tax.
- If the rate is still ₦2,000 per £1, that converts to £5,800.
- If the naira falls to ₦2,320 per £1 (16% weaker), it converts to exactly £5,000, before any conversion fees or UK tax.
- If it falls further, the naira route loses money in pounds.
The break-even point is roughly where the naira's fall matches the interest gap. Nobody can tell you in advance which side of that line a year will land on.
How to decide
- Money you will spend in the UK (rent, emergencies, a deposit on a flat) belongs in pounds, and an ISA is the obvious home once your allowance-free interest runs out.
- Money you will spend in Nigeria (building, school fees for relatives, a return move) is already exposed to the naira, so holding it in naira is matching, not speculating.
- Splitting by purpose is usually safer than chasing the higher number. Our guide to splitting savings between pounds and naira goes further.
Where Pryme fits
Pryme does not offer ISAs. For the naira side, a Pryme account holds naira alongside pounds, and naira Savings Boxes (Flexible, Fixed, Investment and Interest-free) show their current rates in the app. Naira deposits are held by a licensed Nigerian microfinance bank, regulated by the CBN and insured by the NDIC up to the applicable limit. Swap shows the rate before you convert.
Questions people ask
Can I open an ISA if I am on a UK visa?
GOV.UK requires you to be 18 or over and resident in the UK; it does not list nationality or visa type as a condition. Check the provider's own ID requirements.
Is naira interest taxed in the UK?
If you are UK resident, GOV.UK says you are normally taxed on all your income, including interest earned in Nigeria. The UK-Nigeria treaty gives credit for Nigerian tax paid. This is information, not advice.
What happens to my ISA if I move back to Nigeria?
You can keep it and the UK tax relief, but you cannot pay in while non-UK resident, and you must tell your provider.
Is a 16% naira rate better than 4% in the UK?
Only if the naira does not fall by more than the gap before you convert back. Compare outcomes in the currency you will spend.
Sources
- GOV.UK: Individual Savings Accounts (updated 30 Sep 2026) · accessed Oct 2026
- GOV.UK: ISAs, if you move abroad · accessed Oct 2026
- GOV.UK: Tax on savings interest, how much is tax free · accessed Oct 2026
- GOV.UK: Tax on foreign income, residence (updated 1 Oct 2026) · accessed Oct 2026
- GOV.UK: 1987 UK-Nigeria double taxation agreement · accessed Oct 2026
- Nairametrics: DMO raises N968.47 billion as 364-day stop rate falls to 15.85% (7 Oct 2026) · accessed Oct 2026
This article is general information, not financial, legal or tax advice. Products described are provided under the terms on this site and are subject to regulation and eligibility.