The famously unforgiving UK bond markets will be eyeing closely what happens during another day of scrutiny for Sir Keir Starmer as former top civil servant Sir Olly Robbins prepares to answer questions on the appointment of Lord Peter Mandelson as US ambassador.
The warning from Nigel Green, the CEO of global financial advisory giant deVere Group, comes as political pressure intensifies in Westminster and investors weigh the implications for fiscal credibility and market stability.
At the centre of the controversy are serious questions over what the Prime Minister knew about Lord Mandelson’s past associations, including links to Jeffrey Epstein, alongside concerns about the handling of sensitive government information and reported connections to foreign business interests in jurisdictions such as China and Russia.
The issue has rapidly escalated beyond an appointments row into a test of judgement at the highest level of government.
“Bond markets don’t react to headlines alone, they react to what those headlines imply about the UK government’s control, discipline and credibility,” says Nigel Green.
“Today’s developments go directly to those fundamentals.”
Memories of the Liz Truss-era gilt crisis remain vivid.
In 2022, yields surged at extraordinary speed following the mini-Budget, forcing emergency intervention and exposing the fragility of investor confidence.
“Truss remains the benchmark for political risk in UK markets,” he explains.
“Investors have seen how quickly things can unravel once credibility is in doubt.
“This experience has permanently changed how gilts are priced.”
Current conditions leave little margin for error. UK government debt sits near 100% of GDP, while borrowing costs remain significantly higher than the ultra-low rates of the previous decade, with 10-year gilt yields still around the 4% mark.
“Investors are already demanding a premium to hold UK debt,” he says. “Any additional uncertainty, especially around leadership stability, feeds directly into that pricing.”
Attention is now fixed on whether the pressure surrounding the Prime Minister begins to erode broader political cohesion.
“A leadership challenge before the May elections remains unlikely at this stage,” notes Nigel Green.
“But the ground is clearly unstable. Markets are alert to the possibility that a misstep today could mark the start of a deeper unravelling.”
The implications for Chancellor Rachel Reeves are central to the market calculus.
The deVere CEO affirms: “Rachel Reeves has built credibility on predictability and fiscal discipline.
“Investors view the Prime Minister and Chancellor as a single economic framework. If that framework comes under strain, confidence weakens immediately.
“Any perception that the Chancellor’s position could become uncertain would trigger a reassessment across bond markets.”
Speed remains critical. Markets have shown they move ahead of political confirmation.
“Investors don’t wait for official announcements,” he says. “They respond to signals. Signs of fragmentation, briefing wars, or slipping authority can drive yields higher within hours.”
International capital flows add further sensitivity. Overseas investors hold a substantial portion of UK gilts, and their reaction can amplify moves.
“Global investors are highly responsive to risk. If stability comes into question, capital reallocates fast. The UK competes for that capital every day.”
Short-term outcomes hinge on how today’s scrutiny unfolds, particularly whether Sir Olly Robbins’ testimony introduces further contradictions or pressure points.
“Momentum is everything. If today reinforces concerns about leadership judgement or control, markets will escalate their response. If it stabilises the narrative, the reaction may be contained.”
The broader risk, however, extends beyond immediate headlines.
Nigel Green concludes: “This has the potential to become a defining moment.
“The UK bond markets are already assessing whether the foundations are weakening.
“If confidence begins to fracture much further, gilts will reflect it long before politics catches up.”