The Bank of England will stop accepting bonds linked to thermal coal as security when commercial banks borrow from it, a change that takes effect in October and was announced quietly earlier this summer, the Guardian reported.

The mechanism is unfamiliar to most people outside banking, and it is the whole story, so it is worth setting out plainly.

What collateral does

Central banks lend to commercial banks routinely, not only in emergencies. The Bank of England regularly issues loans to institutions such as Barclays, Lloyds, NatWest and HSBC so they can settle transactions and keep operations running smoothly.

Those loans are secured. The borrowing bank pledges assets, usually bonds, which the central bank keeps if the loan is not repaid. The central bank decides which assets it will accept and how much it will lend against each one, applying a discount known as a haircut.

That decision is more powerful than it sounds. An asset a central bank will accept is an asset a commercial bank can always convert into cash, which makes it more attractive to hold, which supports its price and lowers the issuer's borrowing costs. Removing an asset from the eligible list quietly withdraws that advantage.

What has changed

Bonds connected to thermal coal, the grade burned in power stations to generate electricity, become ineligible. The Bank has also said it will discount the value of bonds in other relevant sectors "to protect the Bank against financial risks."

The Bank's stated rationale is risk, not climate policy. Its policy statement says thermal coal companies "can be exposed to potential financial risks connected to the adjustment of the economy towards net zero," which is the argument that assets tied to coal may lose value as economies move away from it, leaving the central bank holding weakened security.

The direct effect is modest

Britain is not a significant thermal coal producer and closed its last coal-fired power station in 2024, so few UK issuers are directly affected. More importantly, corporate bonds are a small part of what banks actually pledge: central bank collateral is dominated by government securities, so the number of coal-linked bonds being handed over on any given day was never large.

This is why the change is best read as a signal rather than a funding shock. Around 150 of the world's largest financial companies already apply some form of restriction on business with the thermal coal industry, according to figures published by the non-profit Reclaim Finance last September, so the Bank is joining a direction of travel rather than setting it.

Campaigners nonetheless treated it as significant. "It's a strong signal from a central bank, and to the market as well," Ellie McLaughlin, a senior policy and advocacy manager at Positive Money, told the Guardian. The hope among activists is that it pushes commercial banks to reconsider holding coal-linked assets at all.

The argument this opens

There is a genuine dispute here, and it is not really about coal.

One view is that this is ordinary risk management. Central banks already refuse plenty of assets and apply differential haircuts based on credit quality and liquidity. If an asset class faces a foreseeable structural decline, declining to lend against it is the same prudential judgment applied to a new risk.

The other view is that collateral eligibility is an instrument of industrial policy wearing technical clothing. Deciding which industries get privileged access to central bank liquidity shapes their cost of capital, and doing so through an unelected institution sidesteps the legislature that would normally make that call. On this reading, the precedent matters more than the coal: once the framework can encode transition risk, the question becomes which sector is assessed next, and by whom.

Both positions are coherent, and where a reader lands depends largely on whether they regard climate transition as a financial risk that central banks are obliged to manage, or a policy objective they should stay out of.

What to watch

The practical question for markets is whether other central banks converge on exclusion or on pricing. Excluding an asset outright is a blunt instrument; applying a larger haircut achieves a similar effect while keeping the asset usable, which is closer to how collateral frameworks normally handle risk. The Bank has done both, banning coal outright while discounting other exposed sectors.

If that combination becomes the template, the more consequential half is probably the haircuts, because they can be extended across many sectors by degree rather than by prohibition, and with far less public argument.