When Sir Steve Webb introduced the triple lock as Lib Dem pensions minister in the coalition government, the aim was to close the gap between the state pension and average earnings and reverse years of real-terms decline during which the state pension had not kept up with living costs.

In 2010, the basic state pension was just £97.65 per week, or just over £5,000 per year, for a single person – a truly pitiful amount for someone who had worked for at least 39 or 44 years (depending if you were a man or a woman), even when you consider the greater prevalence of employer defined benefit pension schemes at the time.

Meanwhile, the median gross annual salary for full-time employees at the same point was around £26,000, meaning the state pension represented less than 20% of average earnings.

The triple lock uprates the state pension in line with the consumer price index (inflation), average wage growth, or by 2.5% – whichever is highest – meaning the gap between the state pension and average earnings has slowly closed.

The basic state pension is now £184.90 per week or £9,614.90 a year, while the new state pension (introduced in April 2016 for men born on or after 6 April 1951 and women born on or after 6 April 1953) is £241.30 a week, or £12,547.60 a year.

This compares with a median gross annual salary of £39,039, meaning the basic state pension represents 25% of average earnings, while the new state pension is 32%.

This increase, and the associated drop in pensioner poverty, is welcome. However, the triple lock, and the ratchet effect it creates of the state pension rising faster than both average salaries and the tax revenue required to fund it, is unsustainable over the long term. The parlous state of the public finances and an ageing population mean it cannot be allowed to go on in perpetuity.

The questions we need to ask are: at what point has the triple lock fulfilled its purpose and, once it has, how do we ensure that the state pension keeps up in a fair and equitable way?

I don’t have an immediate answer to either of those questions. I do know we need to start having the conversation, though. It’s vital to build some level of cross-party consensus ahead of the 2029 general election. Otherwise, the risk is that political inertia and a fear of alienating pensioners sees the triple lock recommitted to for a further five years, further exacerbating the fiscal situation and adding to intergenerational inequity.

Theresa May’s decision to launch plans for reform of social care – dubbed the “dementia tax” by opponents – in the heat of an election was the beginning of her downfall and arguably cost her party a majority in 2017.

Similarly, Sir Keir Starmer’s government failed to roll the pitch for the proposal to cut winter fuel payments and hasn’t recovered from it, despite – in my humble opinion – that policy having significant merit.

Setting the scene for ending the triple lock won’t be popular. However, with Labour in disarray, Reform pushing a populist agenda, and the Conservatives constantly looking further right, there is an opportunity for the Lib Dems to show they are the grown ups with a long-term, economically sensible, and fair outlook.

* Adam Shaw is a Liberal Democrat member residing in West Lothian.