The Prime Minister insists the reform is necessary to help create a new National Care Service, arguing that Britain can no longer continue with a social care system that leaves families facing potentially enormous bills when an elderly relative becomes seriously ill or requires long-term support.
But pension campaigners, opposition parties and trade union figures have questioned whether pensioners should be expected to pay for that ambition.
The disagreement goes to the heart of a much bigger question: how should Britain fund its ageing population while protecting those who have already retired?
Under the current triple lock, the state pension rises each year by whichever is highest of inflation, average earnings growth or 2.5 per cent. The mechanism was introduced as a safeguard against pensioners seeing their income fall behind the wider economy.
Burnham’s proposed system would remove the earnings element. Instead, the state pension would rise by inflation or 2.5 per cent, whichever is higher.
That means pensioners would still have some protection against rising prices, but they would no longer automatically benefit when wages increase significantly faster than inflation.
For supporters of the reform, that is a necessary adjustment to a system that has become increasingly expensive.
Britain’s demographic profile is changing rapidly. People are living longer, while the number of pensioners is increasing relative to the working-age population. At the same time, the Government is under pressure to fund the NHS, social care, pensions, housing and other public services.
Maintaining an uncapped earnings-linked guarantee indefinitely could therefore place an increasing burden on future taxpayers.
Burnham is attempting to argue that the reform should not be viewed as a straightforward pension cut.
If inflation remains high, pensioners would continue to receive increases based on the cost of living. The minimum 2.5 per cent guarantee would also remain in place.
The real change would come when wages rise faster than prices.
That is precisely what worries opponents.
Pensioners who have spent decades contributing through taxes and National Insurance may reasonably expect their retirement income to maintain its position relative to the rest of society. Removing the earnings element could gradually cause the state pension to fall behind average wages.
Over a single year, the difference might appear relatively small.
Over many years, however, the cumulative effect could become much more significant.
That is why the announcement has generated such a strong political reaction.
Reform UK has already promised to protect the triple lock, while the Conservatives have repeatedly committed themselves to the same principle. That puts Labour in an uncomfortable position.
The Government must now convince voters that its alternative offers something more valuable than the existing guarantee.
Its strongest argument is social care.
The current care system has long been criticised for placing heavy financial pressure on families. Depending on individual circumstances, people can be required to contribute substantial amounts towards care costs.
Burnham has argued that this is fundamentally unfair.
A person can spend a lifetime working, paying taxes and saving for retirement, only to discover that a serious illness or disability can rapidly consume those savings.
In the most extreme cases, families fear that an elderly relative could lose much of the wealth accumulated over decades.
The proposed National Care Service is intended to change that.
Burnham wants care to be available free at the point of use, creating a system in which people contribute collectively rather than facing potentially devastating individual bills.
That is an attractive proposition for many families.
Most people will either need social care themselves or have a parent, partner or relative who requires it at some stage.
The difficulty is the price.
A nationwide care service would require substantial and sustained funding. Even if the Government finds savings through reduced hospital admissions and other efficiencies, it is unlikely to be cost-free.
That leaves taxpayers facing an uncomfortable choice.
Should Britain maintain stronger pension guarantees while accepting that social care will remain partly funded through individual contributions?
Or should the state provide much more generous social care, with pensioners accepting a slower increase in their retirement income as part of the bargain?
This is why Burnham’s decision is likely to become a major electoral issue.
Pensioners are among the most politically engaged groups in Britain. They vote in large numbers and are acutely aware of changes affecting their income.
The memory of previous disputes over pension support is also likely to influence the debate.
The controversy surrounding the Winter Fuel Payment remains fresh for many older voters. Changes to eligibility produced significant political pressure and demonstrated how quickly pension policies can become electoral flashpoints.
Burnham will therefore need to avoid creating the impression that pensioners are simply being used as a convenient source of savings.
His argument must be that older people will ultimately benefit from a more secure system of social care.
Opponents will make the opposite case.
They will argue that pensioners have already paid into the system throughout their working lives and should not be asked to surrender an important protection because successive governments failed to resolve the social care crisis.
There is also a question about fairness between generations.
Younger workers face high housing costs, student debts and taxes, while pensioners may own property and have accumulated assets over decades.
Critics of the triple lock argue that the policy can transfer resources towards older generations at a time when younger households are struggling.
But supporters respond that not every pensioner is wealthy.
Millions rely heavily on the state pension and have limited savings. For these households, even relatively modest changes in annual income can have a direct impact on their ability to pay for food, heating, transport and other essentials.
The debate therefore cannot simply be reduced to “rich pensioners versus poor workers”.
There are wealthy retirees and financially vulnerable retirees, just as there are high earners and struggling young families.
That complexity will make Burnham’s task even harder.
Another important issue is whether the reform actually delivers enough money to transform social care.
If pension changes generate only part of the funding required, taxpayers may eventually face further measures.
That could mean higher income taxes, changes to inheritance tax, alterations to National Insurance or other revenue-raising measures.
This is one reason opposition parties are already questioning the Government’s calculations.
They want to know the full cost of the National Care Service and exactly how much of it will be funded by changes to the triple lock.
The Government will also have to explain what happens if inflation rises sharply.
The proposed model retains inflation protection, but the political pressure on ministers could become intense if pensioners see their real income squeezed by rapidly increasing costs.
Conversely, if wages rise substantially while inflation remains low, pensioners could find themselves receiving smaller increases than working households.
That is the central trade-off.
Burnham is effectively replacing one form of protection with another.
Instead of guaranteeing that pensioners share automatically in whichever measure grows fastest, he is prioritising protection against inflation while redirecting some potential future spending towards social care.
Whether that is a sensible reform or an unfair attack on pensioners is now for voters to decide.
The Prime Minister has presented the change as part of a much larger attempt to rebuild Britain’s welfare state.
Opposition politicians see it as evidence that Labour is prepared to break promises when confronted with the reality of the public finances.
The argument is unlikely to disappear before the next election.
For pensioners, the question is whether the security offered by a National Care Service is worth giving up part of the protection provided by the triple lock.
For younger taxpayers, the question may be whether the existing pension system is affordable without placing an ever-greater burden on future generations.
And for Burnham, the political challenge is to persuade both groups that his approach is not simply a way of moving money from one part of the welfare state to another.
With the triple lock now firmly at the centre of the national debate, voters have a straightforward choice to consider: