Public sector pensions is an issue that causes concern and even anger, but very few of us can claim to really understand it.

The funding of retirement provision for government employees is a complex subject beyond the comprehension of most ordinary mortals.

But you don’t need to be an expert to spot the giant caterpillar of staff pension debt eating its way towards the budget for the island’s public services.

It is on course to arrive there in four years time, to take a first bite of £45 million and to keep on munching annually for many decades into the future.

Tynwald has been searching earnestly for a politically acceptable way of dealing with the voracious beast, and is due to make a decision at its March sitting.

Members should be realising by now that this monster cannot be killed off, even though one or two of them may have given the impression in the past that it could be slain.

All they can do is try to curb the creature’s appetite, camouflage it and learn to live with an unwanted presence that will be around for the rest of the century.

For the caterpillar represents a colossal debt that has already been incurred, the result of historic mismanagement on a monumental scale.

The debt can only be avoided by measures too extreme for Manx politicians to stomach.

Explaining all this to the public will be tricky.

But the current crop of MHKs are reasonable folk and they are hoping for an understanding electorate.

I should declare an interest here as the recipient of a modest government pension.

It is not my intention to defend the system, however, but to consider the implications of one of the biggest issues in island politics.

The scariest statistic about public sector pensions, one often quoted, is the overall liability of £3.7 billion.

This is a hypothetical sum that would only materialise if all the pension money owed had to be paid out at once, which is not scheduled to happen.

The big difficulty Tynwald is wrestling with is the ’legacy funding gap’.

This is the shortfall between contributions coming into the scheme, from current employees and from government as the employer, and the amount being paid out to pensioners.

It is now too late to resolve the problem quickly by simply increasing the former and reducing the latter.

The funding gap has built up over the past 25 years, a period which saw expansion in public services and significant increases in staff numbers and salaries.

Successive Manx governments failed to ensure that pension scheme income would match expenditure when all these public servants started to retire, and to live longer in retirement as life expectancy improved.

It is tempting to speculate that this lack of provision was one of the many flaws obscured by the largesse of the island’s previous VAT sharing agreement with the United Kingdom.

However, the UK and other countries have had similar pension challenges so the issue is by no means unique to the Isle of Man.

In recent years the funding gap has been filled from a pensions reserve which is expected to run out in 2022.

At that point the burden is set to fall on the revenue budget, which pays for important services like health, education and social care.

The strategy so far has been to clear enough space in the revenue budget to accommodate the funding gap without it impinging on other spending.

This optimistic approach assumes the economy and tax receipts will stay buoyant in the turbulent aftermath of Brexit.

Pressure on service budgets is inevitable, and it will draw resentful attention to the chunk of money ring-fenced for the public servants’ pensions deficit.

It is naive to hope the public will compare this £45 million to overall annual revenue spending of £1,000 million, and agree it is a relatively small sum in the greater scheme of things.

They will compare it to health underfunding of much lesser amounts, or to an education budget of £100 million, and ask what the £45 million could achieve in our hospitals or schools.

Vigilant MHKs will note the timetable for staff pension debt to move in to the same financial space as health, education and other valued services.

The change is due one year after the next general election, at which sitting members may have to defend it against rival candidates playing to public indignation.

Paying the debt from revenue is politically dangerous but alternatives like large-scale borrowing or continuing to use reserves still come at a big cost to public funds, though the impact might be less immediately obvious.

Other options could help to mitigate the problem over decades or offer the appearance of tough political intervention while making little practical difference.

So why doesn’t Tynwald just renege on the debt, stand up to the retired fat-cat civil servants and take their generous pensions off them?

Cutting back on the pension benefits that have already been promised to employees is the nuclear option.

It is the drastic step taken in Ireland during the financial crisis in that country.

The Manx government has received legal advice that a similar move here could be blocked in the courts as a last resort only justified by an economic emergency, which is not the same thing as a political dilemma.

MHKs know better than to dismiss pension scheme members as an unpopular minority or pampered elite.

The group includes manual workers and public servants that people actually appreciate, like medical staff, as well as the friendless civil service, which is only one third of the total government workforce.

A succession of reforms in the past few years has seen existing staff paying more in contributions for less in future benefits, and this will help to narrow the deficiency in the longer term.

There is concern, though, that if this process is pushed too far it could damage recruitment and retention in critical areas such as health.

Most public sector pensions are not high enough to make headlines. Of the 6,500 currently in payment, 4,000 are below £10,000 a year.

About 70 are above £50,000, some way beyond that level and harder for the less fortunate to accept.

A key statistic in this debate is the extraordinarily large number of island residents who are, or will be, enjoying a government staff pension.

The total is 21,000.

Anxious politicians may view this figure in the context of a national registered electorate of 60,000, or the 32,000 who voted in the last general election.

So MHKs cannot afford to alienate the beneficiaries of public sector pensions.

But they could lose other votes if the cost of those pensions is seen to threaten services that people care about.

In a period of unprecedented economic uncertainty Tynwald will be gambling on there still being enough resources to keep everyone happy.

That doesn’t look like a safe bet.