Thames Water has gained support from its top-ranking creditors to proceed to the next stage of securing a £3bn emergency funding package intended to stave off its collapse for at least a year.

The struggling utility company said on Wednesday that 75% of the holders of its least risky loans – known as class A debt – had backed a plan to extend the cash lifeline, the minimum threshold needed to receive court approval for changes to its debts.

Thames faces the prospect of a temporary nationalisation if it ultimately collapses, and the emergency funding would help the company avoid a short-term cash crunch.

The support will smooth the path for court hearings to decide whether to approve the deal to take place.

Another group of creditors, who hold riskier class B debt, have offered a competing deal, but Thames Water has so far endorsed the class A offer. Thames said reaching the 75% threshold meant that it could push ahead with a first court date on 17 December.

Thames Water provides water and sewage services to 16 million customers across London and the Thames Valley in south-east England. It has been on the verge of collapse for several months, labouring under its £15bn debt pile.

Securing the emergency cash would give Britain’s biggest water company time to try to raise the billions of pounds of new equity investment it needs to return to a more stable footing.

Thames Water said receiving the support was “an important milestone” in securing the emergency cash. It also said that it appeared to have secured the support of enough creditors to access a £400m reserve account, in a parallel process.

Even if Thames secures formal backing from its creditors to access more funding, there are several further hoops to jump through. It must go through a formal court process, and the backing of creditors ultimately depends on the outcome of its negotiations with the industry regulator for England and Wales, Ofwat.

Thames has been in talks with the regulator, along with other water companies, over how much they can increase bills to consumers over the next five years.

Ofwat is expected to give its final verdict on bill increases in December, and investors will compare it with the company’s forecast costs in order to calculate whether to lend Thames extra funds or make equity investments in the water supplier.

A spokesperson for the class A bondholders said: “This is a decisive vote of confidence in the first stage of our restructuring plan for Thames Water from a large group of its creditors, which include a significant number of long-term infrastructure investors.

“It shows that there is a genuine will to develop a market-based solution which saves UK taxpayers from shouldering the costs of special administration.

“Our group is working intensively with the company and providing it with the resources and turnaround expertise it needs to ultimately attract strategic equity and rebuild so all parties can focus once again on delivering a better service for customers and the environment.”

Thames said it was working on getting other creditors – the class B bondholders – to join the class A deal.

A spokesperson for the class B bondholders said: “Even with Thames Water having apparently reached 75% support among its class A creditors for the class A proposal, this is only approval of one of the many classes that will have to ultimately vote on the plan.

“In addition, this level of support is only the bare minimum required for the court to even consider granting its approval. The court will have to carefully consider matters such as fairness and alternatives when deciding whether to approve the non-consensual plan.”

The class A bondholder group includes the controversial US hedge funds Elliott Partners and Silver Point, as well as some well-known UK fund managers, representing £12bn of Thames’s debt.