Troubled utility giant Thames Water remains embroiled in discussions regarding a crucial rescue package with its creditors, even as it reports a surge in revenues alongside a rise in customer complaints stemming from increased bills.

Thames Water said it said it cut pollution spills by a fifth, as profits reached £414m for the six months to September – having raised fees substantially – by almost a third (31 per cent) earlier this year.

The group said customer complaints surged by three-quarters to 55,158 in the half-year, as revenues hit close to £2bn for the period.

Despite the return to profit there remain concerns over the ongoing viability of the firm which has around a £17.5bn debt load.

In addition, the most recent financial filing revealed Thames Water had paid £57m across six months in fees towards advisers on the rescue process, including bankers, lawyers and PR consultants.

The heavily indebted company, which serves approximately 16 million customers across Britain, described ongoing negotiations as “positive” but confirmed they are still underway with both the Government and regulators. The aim is to finalise a deal that will stabilise the firm and address its precarious financial state.

Thames Water is currently engaging with a consortium of its primary creditors, London & Valley Water, whose proposal includes injecting capital and writing off debt in exchange for more flexible performance targets.

But Thames Water warned there was still a “material uncertainty” over whether the deal would be secured.

It said: “Since the proposal was made, positive discussions are ongoing between the consortium, the regulators and Government, albeit there remain a number of items to be negotiated and agreed before a recapitalisation can proceed.”

The group is hoping to secure the deal to stave off temporary nationalisation after being left on the brink of collapse by nearly £20 billion of debt.

Its creditors – which include institutional investors such as Aberdeen, Elliott Management and Silverpoint Capital – is seen as the final realistic option on the table to avoid being placed into the Government’s special administration regime after a previous rescue deal with US private equity giant KKR collapsed in May.

Chris Weston, chief executive of Thames Water, said: “We continue to work closely with stakeholders to secure a market-led solution that we believe is in the best interests of our customers and the environment.

“This in turn will allow the transformation of Thames to continue, a programme that will take at least a decade to complete and will restore the infrastructure and operations of the company.”

Half-year results from the provider revealed underlying earnings surged to £1.2 billion for the six months to September 30, compared with £715.1 million a year ago.

Revenues rose by 42% thanks to the bill increases, which it said also helped fund £1.3 billion of capital invested to fix leaks, cut sewage spills and improve water quality.