Deutsche Bank estimates that subtracting the rebate will reduce the Retail Prices Index, which determines payments on UK inflation-linked debt, by about 2.7 percentage points. That would lower the debt interest bill by around £14 billion this year, according to Bloomberg calculations based on Office for Budget Responsibility data. RPI is also tied to some consumer products, such as mobile phone tariffs.

Such savings would be welcomed by the government, which is under intense pressure to spend even more in response to the surge in energy costs. A similar reduction in the Consumer Prices Index, and a potentially lower path for interest rates as a result, could also save the government billions.

Based on CPI, UK inflation is already above 10%. The Bank of England forecasts that it will top out just above 13%, although a surge in gas prices in recent weeks mean officials will almost certainly have to increase that forecast. That means the ONS decision may impact the peak rate this winter, but not change the direction of the outlook for prices. 

Eoin Treacy's view

Persistent inflation has a long tail. The longer it lasts, the greater the effects for government finances in future. Index-linked pensions, tariffs and utilities all push higher with a lag from a current bout of inflation. That’s both a near-term headache and medium-term challenge for most governments. That greatly increases potential for government intervention. It is starting with subsidies and will quickly transition to price caps if prices fail to decline. 
UK Gilts hit a new recovery high today and the market is short-term oversold. The move has to be measured against the increasing surety of a recession. Generally, inflation falls when economies contract.

Of course, there are mitigating circumstances to consider such as energy inflation but slowing global growth could take care of that. For example, China is now exporting unused (Russian) gas to Europe for a tidy profit.   

This report by Francesco Bianchi at Johns Hopkins University and Leonardo Melosi at Federal Reserve Bank of Chicago may be of interest. Here is the abstract:

Low and stable inflation requires an appropriate fiscal framework aimed at stabilizing government debt. Historically, trend inflation is critically influenced by actual or perceived changes to this framework, while cost-push shocks only account for short-lasting movements in inflation. Before the pandemic, a moderate level of fiscal inflation has counteracted deflationary pressures, helping the central bank to avoid deflation. The recent fiscal interventions in response to the COVID pandemic have altered the private sector’s beliefs about the fiscal framework, accelerating the recovery, but also determining an increase in fiscal inflation. This increase in inflation could not have been averted by simply tightening monetary policy. The conquest of post-pandemic inflation requires mutually consistent monetary and fiscal policies to avoid fiscal stagflation.

This research suggests the actions of taxing authorities will be at least as influential as central banks in getting inflation back under control. This greatly enhances the scope for overt government interference in markets.
UK Natural Gas has posted a peak of at least near-term significance.