The yield on 30-year UK government bonds – also known as gilts – reached a new high not seen since 1998 on Wednesday morning, at 5.746% at one stage, up from 5.698% at Tuesday’s market close.
Gilt yields move counter to the value of the bonds, meaning their prices fall when yields rise.
The pound, which suffered hefty losses on Tuesday, was also down again, falling 0.1% to 1.338 US dollars and off 0.1% at 1.148 euros.
It comes amid a bond sell-off globally, with European and US government bonds also under pressure due to political uncertainty and public finance concerns, while Japan was the latest to see its 30-year yield sent soaring as it hit an all-time high on worries over rising debts.
Rising yields on these bonds mean it costs more for governments to borrow from financial markets.
But experts believe a driver of weakness in the UK bond market could be a delayed reaction to the Prime Minister’s Government reshuffle on Monday.
No 10 insisted on Tuesday that Chancellor Rachel Reeves’s authority was not being dealt a blow by Sir Keir’s shake-up in a bid to calm market jitters.
This week’s reshuffle saw the Chancellor’s deputy, Darren Jones, move into a new role as chief secretary to the Prime Minister.
Health Secretary Wes Streeting told Sky News: “The Chancellor, since she came in last year, has been determined to restore stability to our economy, to get growth back into our economy, and to create the conditions where we can get the nation’s finances back to health.”
He said while there are “encouraging signs”, there is “much more to do”.
Mr Streeting added: “Britain is not out of the woods, and that is why the discipline and the focus that she has brought on cost of living, on economic growth and creating the conditions for businesses to be successful is really important, and the discipline we show as a Cabinet in terms of public spending is really important.”
London’s FTSE 100 Index edged 22.2 points higher at 9138.9 on Wednesday morning, despite the bond woes, while gold hit new record highs once again – above 3,530 US dollars – as nervous investors flocked to the safe haven asset.
Kathleen Brooks, research director at XTB, said the “focus is likely to remain on the budget for some time” as bond markets look for reassurances on how Ms Reeves will plug a black hole in the nation’s public finances – estimated by some to be as much as £51 billion.
She said: “UK bond yields have been on an upward trajectory for most of this year and have risen significantly since Labour took office.
“The bond market will need some hefty persuading that Labour will reign in public sector spending and bring the UK’s finances under control.
“This is why we expect to see bouts of UK bond market volatility in the coming months.”