A more useful question than “which bond ETF is best?” is “what job is the bond holding there to do?” It helps to separate three jobs: steadying a portfolio in sterling, holding UK government bonds of a chosen duration, and spreading bond holdings across many markets.
Hold UK government bonds only, in sterling, so the bond holding moves with UK interest rates and carries no currency risk.
Spread the bond holding across many countries and across government and corporate bonds. For a sterling investor the share class’s hedge matters: AGBP is hedged to sterling, while AGGU, another class of the same iShares fund, is hedged to US dollars.
| What you need | Type of fund often used | Why |
|---|---|---|
| A UK-government sleeve with clear sterling framing. | Gilt ETF | That is the cleanest expression of the job and the least confusing definition of the sleeve. |
| Broader bond diversification across markets. | Global aggregate bond ETF | The global route gives you more than just one sovereign market and one yield curve. |
| Shorter-duration cash alternative. | Short-duration or money-market style product | Neither long gilt exposure nor a big global aggregate sleeve is automatically a good parking place for near-term spending money. |
| A defensive sleeve for a simple long-term portfolio. | Whichever route you can explain and stick with | A bond holding whose duration, currency treatment and contents are understood is easier to hold through a period of rising interest rates. |
For bonds, currency noise can dominate the outcome more than people expect. Hedging matters more here than it often does for global equity funds.
The difference between a short-duration, intermediate and long-duration bond sleeve is a real portfolio decision, not a footnote.
Whether you hold gilts or a global bond fund, the single number that explains most of the short-term price swings is duration — a measure, in years, of how sensitive a bond or bond ETF is to changes in interest rates.
The rule of thumb is simple enough to do in your head: for every 1 percentage point move in market interest rates, a bond fund's price moves by roughly its duration, in the opposite direction. A fund with a duration of about 7 years would be expected to fall by roughly 7% if yields rose by 1%, and rise by roughly 7% if yields fell by 1%. A short-dated fund with a duration near 2 years would move only about 2% for the same shift. This is an approximation, not a guarantee — the relationship is not perfectly linear and other factors play a part — but it is widely used as a first approximation.
This matters because long-dated gilt ETFs and broad global aggregate funds can carry quite different durations. A long gilt fund might sit well into double digits; a global aggregate fund is often shorter and more diversified across maturities. Two funds that both sound “defensive” can therefore behave very differently when the Bank of England or other central banks move rates.
None of this makes gilts or long duration “bad”. Longer duration can be exactly what you want if you are trying to lock in a yield for the long term, or if you want the sleeve to rally hard when rates are cut in a recession. The point is to choose duration deliberately rather than discovering it during a bad year.
Tax is one area where gilts have a concrete, often overlooked edge for UK individual investors — and it is worth understanding before you assume two bond funds are equivalent.
This points to a quietly useful piece of asset location: outside an ISA, a directly held gilt with a low coupon, bought below its £100 redemption value, delivers much of its return as a capital gain, which is exempt from CGT, rather than as taxable interest. A global bond ETF’s return, by contrast, comes largely as interest, which is taxable outside an ISA or pension. This is general education, not personal advice — your own position depends on your income, allowances and goals.
Putting duration, diversification, currency and tax together, the decision usually comes down to what you actually need the money to do.
| Your goal | What often fits | The trade-off to accept |
|---|---|---|
| Money you may need in 1–3 years. | Short-duration gilts, money-market style funds, or cash savings | Lower expected return in exchange for far smaller price swings. |
| A diversified ballast sleeve for a long-term ISA or SIPP. | A GBP-hedged global aggregate bond ETF | You accept broad credit and multi-country exposure in return for not betting on a single yield curve, with currency risk hedged away. |
| A clean sterling government sleeve you can explain. | A gilt ETF, with duration chosen to match your horizon | You concentrate on one issuer (the UK government) and one yield curve, and you carry that duration through rate cycles. |
| To reduce the equity rollercoaster, full stop. | Whichever bond route you genuinely understand and will hold | The best ballast is the one you will not panic-sell. Comprehension beats sophistication. |
Whatever the headline, remember the role of bonds in a portfolio: they are there to dampen volatility and provide a different return pattern from shares, not to maximise growth. A bond sleeve that you understand — its duration, its currency treatment, and how it is taxed in your account — will serve you better in an ugly year than a higher-yielding one you cannot explain. None of the above is a recommendation to buy any particular fund; it is a framework for asking better questions.
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