“She clearly has to fix the problem.I think it’s one thing to come back twice.We don’t want to be here a third time.” Bluntness served Ruth Curtice well in her past life as a senior Treasury official.These days, she deploys it publicly, as chief executive of the Resolution Foundation – urging Rachel Reeves to think the unthinkable before November’s crunch budget.

In the course of half an hour’s conversation in her bright white Westminster office, Curtice says the chancellor must be ready to ditch Labour’s manifesto tax pledges, scrap the pensions triple lock, lift the two-child limit on benefits – and forget the idea that a new wealth tax is the answer to anything.As a longtime civil servant, Curtice, 41, served nine different chancellors and rose to be the Treasury’s director of fiscal policy, before crossing St James’s Park earlier this year to run arguably the UK’s most influential thinktank.She emphasises its non-partisan nature, and impact on past policies, including George Osborne’s “national living wage” – but there is no denying its intimate links to the current Labour regime.Curtice’s predecessor, Torsten Bell, is the pensions minister, recently handed an important role in thrashing out plans for the budget.The newbie Treasury minister Dan Tomlinson is a former Resolution Foundation economist.

Richard Hughes passed through en route from the Treasury to the highly influential post of director of the Office for Budget Responsibility (OBR).Keir Starmer’s new economic adviser, Minouche Shafik, co-chaired the thinktank’s weighty Economy 2030 commission.The appointments have prompted accusations that a “leftwing cabal” has taken over the Treasury.Curtice says the thinktank has “no affiliation” with Labour, and that, of the seven Conservative chancellors she worked with, “lots of them care about exactly the group that Resolution care about”.Of her emergence from the anonymity of the Treasury into public life, Curtice says: “I’ve enjoyed it, actually, more than I thought I would.

And, you know, it’s nice to be allowed to say what you think.”Her father is the legendary polling expert Sir John Curtice – a much-loved fixture of TV elections coverage.She says he gave her a love of politics, without the partisanship that can dominate discussion in Westminster.“I feel quite lucky to have grown up in a household where politics was everywhere, but political loyalty was nowhere,” she says.“I guess that’s why Resolution chimes with me and why I feel quite strongly about it.

”When it came to specifics, though, he was less useful.When she showed him a politics-related question she was struggling with during her Scottish highers – the equivalent of A-levels – “he just told me the question was wrong and it was no help at all”.She clearly feels many politicians are also asking the wrong questions in the run-up to November’s budget.“The debate just does feel kind of unrealistic,” she says.“Taxes are going up because the government chose to fund the NHS.

That’s the trade-off.”Reeves used last year’s budget to announce a £40bn package of tax rises, much of which was set aside for spending on healthcare after an election campaign in which tales of hard-to-reach GPs and ambulance queues featured heavily.But the narrow margin of error the chancellor left herself means that an expected forecast downgrade from the OBR is likely to force her to come back for more in November, if she wants to meet her fiscal rules.Curtice is calling on the chancellor to decisively increase the £9.9bn headroom against her fiscal rules, to avoid the risk of constant destabilising speculation about future tax rises.

If necessary, she says, Reeves should consider busting Labour’s manifesto promises to do so.“If she could increase her margin for error against her fiscal rules, that would be a good thing.That’s difficult to achieve, but she probably wouldn’t regret it in a year’s time.”Labour promised before last year’s general election not to increase taxes on “working people”, including national insurance, VAT or income tax, and Reeves has recently reiterated that pledge.But, Curtice points out, “the taxes covered by the manifesto are about 75% of the tax base.

It would be better to think about those than to do things that are economically damaging, and in the end, that might be the way to go.”She added: “Broad-based tax rises should be on the table if that’s what’s needed to fix the picture.” The CBI chief executive, Rain Newton-Smith, made a similar argument recently.Curtice rejects the idea, popular on Labour’s left, that a new wealth tax, levied as a percentage of the total value of a person’s assets, is a feasible way of raising significant new revenue.Instead, she advocates reforming the capital gains tax system to move it more in line with income tax – so unearned income is not treated more generously by HMRC than workers’ wages.

“We do tax wealth: we tax it through capital gains tax and inheritance tax.Let’s do that better,” she said, adding: “It’s just more likely to work, certainly in the short term, than inventing a new tax.”The Resolution Foundation, which celebrates its 20th anniversary this week, is funded by its founder and chair, the insurance tycoon Clive Cowdery – to the tune of £2.5m last year.Instead of the cramped quarters endured by some Westminster thinktanks, it occupies part of a smart townhouse, decked out with chrome and black marble.

Its brief is to advance the living standards of low- and middle-income workers – an aim that has become only more pressing over its two decades of existence.In research published to coincide with the anniversary, the thinktank finds that, had living standards continued to increase over the past 20 years at the same pace of the previous decade – 1995-2005 – typical yearly family incomes would be an extraordinary £20,000 higher.Curtice is keen to point out that this has not been a story of the rich racing away from the rest, but of real incomes stagnating across the entire economy.“Truthfully, the challenge of the last 20 years is not rising inequality.We have, as promised, all been in this together.

It’s been terrible for rich and for poor,” she says,“Now, it’s harder for poor households to bear and they have had the worst time, so we mustn’t forget they’re the only group where living standards have actually fallen through this period,We know that child poverty has risen and is projected to continue to rise,But the stagnation in living standards is very broad-based,”One group that has done relatively well, however, is pensioners – and like Bell before he crossed the line into politics, she is clear that the triple lock, which increases the state pension in line with the highest of earnings, inflation or 2.

5%, should go.“Living standards over the last 20 years for non-pensioners have grown about 7%, [and] for pensioners have grown about 21%,” she says.“Resolution has long said that it would be better to peg pensions to average earnings rather than having this ratchet.”Bell recently ruled the triple lock out of scope for a new pensions commission, set up to report to the government on how to improve retirement provision in the UK.But Curtice says: “I would find it hard to sit on the pensions commission and not talk about it.

”She saves some of her bluntest language for the challenge of tackling rising child poverty, with the government yet to set out a detailed strategy on how it will achieve this manifesto promise.Like many Labour MPs, including the deputy leadership challenger Lucy Powell, Curtice says there is a straightforward answer to this: scrap the two-child limit that means families are not entitled to child tax credit or universal credit for third and subsequent children – a change that would cost £3.5bn a year.“Lifting the two-child cap is a rare example in public policy of an extremely well-targeted measure.On our projections, child poverty reaches record highs by the end of this parliament.

“Children in large families, half of them will be in poverty.Our job is to produce remarkable statistics, but that one still slightly takes my breath away.”