Burnham’s professed vision of what he has described as ‘Manchesterism’, which draws on his experience as mayor, could also see a significant move towards a greater decentralisation of the energy system, says Matthew. The big worry for utilities, though, is what one of the key themes of this Manchesterist vision - greater control of public services - may mean if it is implemented universally in energy and water.

Among Burnham’s most vocal backers have been left wing campaigners calling for a reversal of Conservatives’ utility privatisations of the ‘80s and ‘90s. An acid test of Burnham’s intentions would be if he allows Thames Water to enter a Special Administration Regime, which the current government has so far resolutely opposed, says consultancy Stonehaven’s head of policy Adam Bell. “If he's a believer in public control, he may view that as being an appropriate option.”

Thames’ investors will therefore be especially eager to get the company’s rescue plan over the line before a possible change of prime minister. There is, however, also a potential “threat” that a beleaguered Starmer may pursue a SAR or nationalisation of Thames in a bid to shore up his position among Labour’s left wing, says a water industry source.

And there are headaches about the impact the current wave of public ownership speculation will have on water companies’ price of debt, they say: “We've got this £104 billion programme of investment, but that's going to be put at risk if companies can't finance it. Even talking about it is going to have real world impact that nobody wants.”

Since declaring his candidacy for the Makerfield by-election, Burnham has said he would stick to the government’s fiscal rules, limiting his scope for potential spending. Holly Brazier Tope, director of politics at the Green Alliance, says: “Realistically at this point in the parliamentary cycle, it feels very unlikely that without a new mandate aka a new election, which no one wants to hold early, he [Burnham] is not going to have a massive amount [of money] available.”

Chris Rumfitt, transport expert and chief executive of public affairs firm Field Consulting, doubts that Burnham’s rhetoric will translate into wholesale nationalisation of the energy and water industries. “The government doesn't have the money to do that and the public wouldn't see any particular direct benefit anyway. You would spend money we don't have, there would doubtless be massive court cases and at the end of it, and I'm not sure the public would notice much difference,” he says, expecting to see the “more pragmatic” approach seen in the “pretty pro-business mayoralty” Burnham has run in Manchester.

Over the weekend, Scottish Power's chief executive Keith Anderson also told The Sunday Times he doesn’t see Burnham going down the nationalisation route. A senior energy source agrees that the economic benefits of restoring public ownership over the industry are not clear. “You're already in a very directed system. With CfDs [Contracts for Difference] and auction rounds, nothing gets built without big government contracts,” they add.

“You couldn't have a much more controlled situation than we're heading to with RESPs and the SSEP,” they say, referring to the regional and statutory spatial energy plans currently being drawn up by the National Energy System Operator (NESO).

Giving NESO an even stronger role than it has now is one of the policy proposals which has been presented to Burnham as a potentially low-cost option for enhanced public control of energy, Utility Week has been told.

Going beyond the current level of control in the energy system could mean copying across the “much stronger” supervisory model being introduced in the water sector, says Bell. This more intensive supervision would raise questions about continuing to have a separate regulator alongside NESO, he says: “There is an argument that in this world you might as well roll Ofgem and NESO together and just have a single body taking charge of the sector because having different bodies just creates friction.”

The downside of such a merger would be less scrutiny and accountability but a “much more straightforward” decision-making process, Bell says: “You are essentially trading off accountability against speed of delivery right now: that might be a trade-off that the government is happy to make.”

One way Burnham could demonstrate his commitment to a greater public role in energy would be to give Great British Energy a supply arm that could compete with the existing private sector retailers, suggests Rumfitt. However, the decidedly mixed experience of the rash of municipal energy suppliers set up in the late 2010s should caution Burnham against going down this route.