Parliament votes today on whether to return to tiered Covid restrictions in England once the four-week lockdown ends tonight.

In a bid to quell disquiet from many Conservative backbenchers, the government published an “Analysis of the health, economic and social effects of COVID-19 and the approach to tiering” last night.

It was supposed to give MPs the information they needed to make an informed decision about today’s vote.

But, despite containing a chapter titled “Economic impacts of tiers”, the document doesn’t actually tell us what effect the policy will have on the economy. It even says: “it is not possible to precisely estimate the economic impacts of any specific restrictions”.

Instead, it sets out three scenarios devised by the independent spending watchdog, the Office for Budget Responsibility (OBR).

In the “upside” forecast, the OBR considers what would happen if Test and Trace were working effectively, the country were in restrictions equivalent to England’s Tier 2 until spring, and a vaccine were widely available shortly after that.

In the “central” scenario, Test and Trace is “partly effective”, vaccines roll out in mid-2021, and the UK is under Tier 3-style rules until spring.

The “downside” imagines what would happen if the Test and Trace system were “ineffective”, regulations were stricter than Tier 3, and no vaccine ever became widely available.

All three forecasts make for sober reading, with a significant fall in GDP and a surge in unemployment in even the best case.

But as the government analysis document says, these scenarios “do not model the precise detail of specific restrictions”.

That’s because each situation contains multiple different assumptions about the progress of the pandemic. It’s not just the tiered restrictions that change in between scenarios: vaccine rollout dates and Test and Trace effectiveness do too.

It’s also possible to have elements from different scenarios happening at once, as the government says, “if the rollout of a vaccine is earlier than expected, then the short-term economic costs may be less than forecast in [the central scenario], and vice versa”. But those variations are not modelled separately.

So we can’t tell from this whether it’s the tiered restrictions themselves or one of those other factors that accounts for the different economic results between the three scenarios.

There’s a further problem, as Dr Flavio Toxvaerd, University Lecturer in the Faculty of Economics at the University of Cambridge, points out. “The key difficulty in analysing the effects of the lockdown is to assess what would happen with the disease and the economy in the absence of restrictions”, he says.

“The Treasury’s release is clear on this important point but stops short of performing the required analysis.”

He continues: “To make things worse, they don’t heed their own advice and in places suggest that government restrictions have had significant impact on the economy. The evidence they present does not support this conclusion, as the economic effects we see are the consequences of both the epidemic and of the restrictions introduced to contain it.”

So the government has published a document that purports to set out the economic effects of the tiered system, but for various reasons, the analysis fails to shed any light, and even claims it’s not possible to make such an assessment.

It leaves us with the thorny question: did the government announce the decision to introduce tiered restrictions in England without first estimating the economic effect of the policy? Or if they did make an assessment, why hasn’t it been published? We put that to the Treasury.

A government spokesperson told FactCheck: “Our COVID-19 Winter Plan puts forward the UK Government’s programme for suppressing the virus, protecting the NHS and the vulnerable, keeping education and the economy going, and providing a route back to normality.

“As this paper sets out, the balance of evidence supports the need for our tiered approach.

“Tiering decisions are based on recommendations from a range of national and regional public health experts and we will continue to work closely with local leaders to drive down local infection rates.”