What happened
The yield on the ten year gilt, the interest rate the British government pays to borrow for a decade, held above 4.9 percent on Tuesday, hovering near its highest level since 10 June. Yields have risen roughly 10 basis points, or 0.1 percentage points, over the past week.
The move is a direct consequence of the oil spike. With Brent crude back above 80 dollars a barrel after Washington reinstated its blockade of Iranian ports, traders have concluded that UK inflation will be higher for longer than the Bank of England assumed, and that the Bank will have to respond.
Money markets now price at least one rate rise from the current Bank Rate of 3.75 percent before the end of the year, with roughly a 25 percent chance attached to a second. That is a striking reversal. The Bank held rates at 3.75 percent at its June meeting, at which point the debate in the City was about when cuts would resume, not whether hikes were coming.
Equities took the news calmly. The FTSE 100 edged up 0.24 percent to 10,497, propped up by energy stocks such as Shell, which gained 2.3 percent. The pound was little changed at 1.3398 against the dollar. Bank shares fared worse, with Lloyds down 1.2 percent.
Why it matters
The gilt yield is the closest thing Britain has to a master interest rate. It is the price the government pays to borrow, and almost every other borrowing cost in the country is stacked on top of it. When it rises, mortgages get more expensive, business loans get more expensive, and the government has less money to spend on everything else because more of the budget goes on interest.
The political timing is uncomfortable. Britain is in the middle of a leadership transition, with Andy Burnham expected to become Labour leader on Friday 17 July and to formally take office as prime minister on Monday 20 July. Incoming governments do not enjoy inheriting a bond market that is testing them.
Rising yields also squeeze the fiscal arithmetic. The Treasury has to refinance maturing debt at whatever rate the market demands, and every 0.1 percentage point of extra yield costs the public purse hundreds of millions of pounds a year over time. That money comes from somewhere, and it usually means either higher taxes or lower spending.
And the loop feeds back on itself. Higher borrowing costs slow the economy, which reduces tax receipts, which increases borrowing, which can push yields higher still. Breaking that loop is the hardest job in economic policy.
Explained simply
A bond yield is a see saw. When the price of the bond goes up, the yield goes down, and when investors get nervous and sell, the price falls and the yield rises. Rising yields are the sound of the market losing confidence.
Here is how it works, step by step. A gilt is an IOU. The government promises to pay a fixed amount of interest each year and give you your money back in ten years. Because the interest payment is fixed, the only thing that can move is the price you pay for the IOU today.
If investors want gilts, they bid the price up, and because the annual payment is fixed, the effective return, the yield, falls. If they do not want them, the price falls and the yield rises. So a yield going up means investors are demanding to be paid more to lend to Britain.
Why would they demand more now? Two reasons. First, inflation. If prices are rising 4 percent a year, a bond paying 4 percent leaves you no better off, so you demand more. Second, expected Bank Rate. If the Bank of England is going to raise its rate, tomorrow bonds will be issued paying more, so nobody wants todays bonds at todays price.
Fixed rate mortgages are priced off this same machinery, through instruments called swap rates that track expected future Bank Rate. That is why gilt yields and mortgage rates move together, usually with a lag of two to four weeks. The mortgage you are quoted in August is being decided in the bond market today.
What it means for you
If you are remortgaging in the next six months, treat this as a warning shot. Lenders reprice fixed deals quickly when swap rates rise. It is standard practice to lock a mortgage offer up to six months before your current deal ends, and most lenders let you switch to a cheaper deal if rates fall in the meantime. Securing an offer now is a free option: you gain if rates rise and lose nothing if they fall.
Tracker mortgage holders are directly exposed. Every 0.25 percentage point rise in Bank Rate adds roughly 13 to 15 pounds a month to a 100,000 pound tracker mortgage over a 25 year term. On a 250,000 pound loan, that is closer to 33 pounds a month per hike, and the market is now pricing at least one.
Savers finally get some good news. If Bank Rate rises rather than falls, the best easy access accounts, currently clustered around 4 percent at challenger banks, should hold up rather than drift lower. This argues against locking cash into a long fixed term bond right now. A one year fix or an easy access account keeps you flexible.
Anyone holding bond funds or a lifestyled pension that has shifted heavily into gilts should understand what rising yields do to them. Bond fund values fall when yields rise. If you are close to retirement and your pension has been automatically de risked into bonds, check what it has actually done this year rather than assuming bonds are the safe option.
The bigger picture
Britain has spent the past two years with among the highest bond yields in the developed world, a legacy of stubborn inflation, weak growth and a bond market that has been unforgiving since the 2022 mini budget episode. Investors have long memories, and the UK still pays a premium for that.
What makes this episode different is that the trigger is external. An oil shock created in the Strait of Hormuz is being transmitted into a British mortgage quote within weeks, and no domestic policy choice can prevent it. All the Bank of England can do is decide whether to lean against the inflation it causes.
Watch the Bank of England August meeting, and watch how the incoming government handles its first encounter with the gilt market. If yields keep climbing towards 5 percent, the pressure to reassure investors will become the defining constraint on everything else it wants to do.
