The decision by debt management offices to shorten duration looked shrewd at the start of this month. With sovereign bonds in the spotlight and UK 30 year Gilts charging to their highest yields since 1998 — within touching distance of 6% — the pivot away from the ultra-long issuance appeared perfectly timed.
In the UK, the DMO saved the Treasury money at precisely the moment investors were repricing fiscal uncertainty, sticky inflation and the fallout from Labour’s local election rout into the long end.
The average maturity of borrowing in the UK is expected to fall to around 8.8 years this year, the lowest this century. Across Europe, sovereign issuers are tilting the same way, insulating government budgets from the rising cost of long-term funding.
The structural rationale is equally defensible. Traditional anchor buyers of long-dated paper — particularly defined benefit pension funds in the UK and Netherlands — are no longer the captive, bottomless pit of demand they once were.
As defined benefit schemes mature and close to new members, their appetite for ultra-long paper has thinned. Debt managers are responding to the market as it is, not the as they wish it still to be.
But that conceals a more uncomfortable truth: shortening duration leaves sovereigns increasingly exposed to liquidity risk. Funding structurally permanent fiscal commitments — pensions, healthcare, debt servicing — with progressively shorter borrowing is the textbook prelude to a refinancing squeeze.
The arithmetic is unforgiving. For a debt stock with an average maturity of under nine years means, in simple terms, roughly an eighth of it needs refinancing every 12 months. That is before a single new pound of borrowing is added. Each rollover is another opportunity for the market to ask harder questions.
Roll the stock long enough, and at some point a window slams shut at precisely the wrong moment. The mechanism seizes, price discovery breaks and the train risks crashing.
Commercial banks guard against that type of asset-liability mismatch with devotion, and regulators force them to. Sovereigns do not face the same discipline. But the bond market, which as this month’s move to multi-year highs reminded everyone, tends to sound its warnings loudly.
Shortening duration can help dodge a political-driven yield spike, but is not the same as solving the problem of guaranteeing cheap funding.