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What the tiny letter you've never noticed on your electricity bill actually means

A small letter in a box on your electricity bill is of potentially huge significance. (Yahoo News UK)
A small letter in a box on your electricity bill is of potentially huge significance. (Yahoo News UK)

Millions of households are monitoring their energy bills more closely than ever before amid the cost of living crisis, with almost half - 42% - of Britons are now struggling to afford them.

Even with increased inspection, though, there is probably one detail you’ve never noticed. It’s a small box normally near the top of the bill containing a single capital letter.

It looks unassuming enough, and there’s no explanation as to what it means. But this letter actually carries huge potential significance - it essentially signifies the precise days and times your household with have to go without power in the event of major national electricity rationing.

Here, Yahoo News UK explains why this letter could be important to you in the coming months. And details in a series of charts, below, what days of the week and times of the day you would have your power cut off.

First of all, why does this matter now?

Earlier this month, the National Grid raised the prospect of planned blackouts this winter - for the first time since the 1970s - if gas power plants are not able to keep running.

This is due to concerns over energy shortages, which have been exacerbated by Russia's invasion of Ukraine. Russia supplied 40% of Europe's natural gas but cut off supplies after being subjected to sanctions, thereby destabilising supply chains and pushing prices higher.

National Grid Electricity System Operator (ESO) figures show 44% of Great Britain’s electricity was generated by gas in September, and the concerns revolve around generators not getting enough gas to keep running.

If there is ever an imbalance where demand is higher than supply, or supply is higher than demand, it can cause major breakdowns in the grid and actual physical damage which can take days to repair.

So, in what it said was an “unlikely” scenario, the National Grid ESO said some households and businesses might face planned three-hour outages to ensure the grid does not collapse.

In such an event, the grid would issue a warning to local and regional distributors saying how much demand needs to be cut. It would then be up to these so-called distribution network operators to decide who gets cut off and who does not.

Should prolonged shortages hit, though, this is where government-imposed electricity rationing comes in under the Energy Act 1976 or Electricity Act 1989. It is detailed in a document called the Electricity Supply Emergency Code (ESEC).

Watch: Climate minister says blackouts are 'unlikely' (from 7 October)

Published in 2005 and most recently updated in 2019, the Code ensures fair distribution of rationing.

The document says: “If a prolonged electricity shortage affects a specific region, or the whole country, electricity rationing may be necessary.

“The ESEC outlines the process for ensuring fair distribution nationally while still protecting those who require special treatment, using a process known as ‘rota disconnections’.”

So where does the letter on your bill come into all this?

The letter is defined in the Code as a “load block”, which corresponds to the relevant point of connection on your property’s network.

There are 18 load blocks, with a letter - A, B, C, D, E, G, H, J, K, L, M, N, P, Q, R, S, T or U - given to each one.

In the event of government-imposed electricity rationing, these 18 load blocks are placed into a rotational disconnection schedule made of eight three-hour blocks per day.

Those times are 12.30am to 3.30am (period 1), 3.30am to 6.30am (period 2), 6.30am to 9.30am (period 3), 9.30am to 12.30pm (period 4), 12.30pm to 3.30pm (period 5), 3.30pm to 6.30pm (period 6), 6.30pm to 9.30pm (period 7) and 9.30pm to 12.30am the following day (period 8).

There are 18 levels of disconnection plans, with Level 1 the least severe and Level 18 the most.

The picture below is a Level 1 disconnection…

A Level 1 disconnection. (gov.uk)
A Level 1 disconnection. (gov.uk)

So, if your property is load block E, it would mean a blackout at 9.30am to 12.30pm on a Monday and 12.30am to 3.30am and 6.30pm to 9.30pm on a Tuesday.

The severity increases on a Level 2 disconnection...

A Level 2 disconnection. (gov.uk)
A Level 2 disconnection. (gov.uk)

... with properties facing six more hours of blackouts. On an aforementioned "E" property, there would also be blackouts between 3.30am and 6.30am on a Monday and 12.30pm to 3.30pm on a Tuesday.

A similar pattern of increasing severity follows for the remaining 16 disconnection schedules, which are pictured at the bottom of this page.

At this point, though, it is worth reiterating blackouts of any kind remain an unlikely scenario this winter. Britain has one of the most reliable power networks in the world.

Another important point is that should the government impose rationing, essential "protected sites" are exempt, meaning buildings such as hospitals and food manufacturers would not be part of the rota.

Disconnection plans from Levels 3 to 18

A Level 3 disconnection. (gov.uk)
A Level 3 disconnection. (gov.uk)
A Level 4 disconnection. (gov.uk)
A Level 4 disconnection. (gov.uk)
A Level 5 disconnection. (gov.uk)
A Level 5 disconnection. (gov.uk)
A Level 6 disconnection. (gov.uk)
A Level 6 disconnection. (gov.uk)
A Level 7 disconnection. (gov.uk)
A Level 7 disconnection. (gov.uk)
A Level 8 disconnection. (gov.uk)
A Level 8 disconnection. (gov.uk)
A Level 9 disconnection. (gov.uk)
A Level 9 disconnection. (gov.uk)
A Level 10 disconnection. (gov.uk)
A Level 10 disconnection. (gov.uk)
A Level 11 disconnection. (gov.uk)
A Level 11 disconnection. (gov.uk)
A Level 12 disconnection. (gov.uk)
A Level 12 disconnection. (gov.uk)
A Level 13 disconnection. (gov.uk)
A Level 13 disconnection. (gov.uk)
A Level 14 disconnection. (gov.uk)
A Level 14 disconnection. (gov.uk)
A Level 15 disconnection. (gov.uk)
A Level 15 disconnection. (gov.uk)
A Level 16 disconnection. (gov.uk)
A Level 16 disconnection. (gov.uk)
A Level 17 disconnection. (gov.uk)
A Level 17 disconnection. (gov.uk)
A Level 18 disconnection. (gov.uk)
A Level 18 disconnection. (gov.uk)