Power cuts in Britain are only 'a matter of time' if bosses at the energy system operator do not tackle underlying problems, a whistleblower claimed today.

The anonymous engineer claimed staff in the National Energy System Operator (Neso) control room still rely on pen and paper to forecast electricity demand.

They alleged that workers have to use figures written on A4 notepads along with historical data and weather information, because of inadequate computer systems.

The experienced engineer also criticised Neso's Open Balancing Platform (OBP), which is a digital control system that manages and balances the electricity grid.

They said the OBP was wasting consumers' money because it provides poor visibility of the network and sometimes overlooks using batteries when dispatching power.

It comes after leaked documents claimed the network was close to shutting down on June 23 because of a shortage of wind and solar energy during the extreme heat.

Energy watchdog Ofgem ordered an investigation in July into whistleblowing allegations raised into operational decision-making and record-keeping by Neso.

Now, the engineer has told The Times that they believe the probe will eventually conclude that the system was secure, 'but that doesn't tell the full story'.

They added: 'We were right on the limit and I don't think there's any harm in coming out and saying that. But for some reason the execs came out right away and said, 'We're completely secure'.

'For the investigation, we remodelled what happened that day but I question what we put into the models. The data that was used - ie what energy was available that day - was optimistic.

'We are banking on help from interconnectors to Europe but in reality we cannot rely on that.'

They added: 'Sadly it is just a matter of time before we have a partial blackout. That's what it will take before something is done. Senior management don't seem to be listening. They seem to care more about the image than the system.'

But Neso has rejected claims that employees' operational concerns are routinely ignored as well as the suggestion that power cuts are simply 'a matter of time'.

The operator also denies that Neso's control room relies on paper-based forecasting, as well as the claim that the OBP routinely overlooks cheaper assets.

It comes after whistleblowers claimed to The Mail on Sunday in July that bosses in charge of the grid were putting lives in danger because they refused to admit the system was on the brink of collapse.

Control room engineers said safety breaches were routine and a catastrophic blackout was an 'engineering certainty'.

Accusing bosses of a cover-up, insiders said they spent two years warning executives at Neso and Ofgem that the rush to Net Zero means they have 'lost control of the system' – but no action was taken.

Writing in the MoS last month, energy consultant Kathryn Porter claimed the national grid is 'more fragile than at any time since privatisation in 1990'.

She added: 'Neso would like to operate the grid with reduced levels of 'inertia', the kinetic energy stored in the spinning components of generators that carry on revolving even in the event of them losing power.

'This move is designed to save £96million a year and help the government hit its Net Zero targets. But I consider this to be a very dangerous proposal as it will increase the possibility of blackouts – and I wrote to Ofgem last year to object to it.'

A Neso spokesman told the Daily Mail today: 'We take all allegations extremely seriously but no findings or conclusions of the independent review have been published, so speculation about its outcome should not be presented as fact.

'Neso does not accept the suggestion that employees' operational concerns are routinely ignored. 

'Our forecasting accuracy is regulated and publicly reported, and claims that the Open Balancing Platform routinely overlooks cheaper assets are wrong.'

An Ofgem spokesman said: 'We take the allegations about the operation of the electricity system during the June heatwave, and the associated whistleblowing concerns, extremely seriously.

'We are undertaking a review of how the system was managed during this period to establish whether Neso complied with regulations, and what lessons can be learnt to improve system security for the future.

'Alongside this, an independent investigation will examine the whistleblowing allegations relating to operational decision-making and record-keeping during this period.

'Both reviews will be conducted thoroughly, objectively and transparently. We won't hesitate to act should we need to, and ensure lessons are learned and any improvements are made.'