The cross-subsidisation of a multi-billion-pound sewerage project in the capital is frustrating a St Albans pensioner who has taken Thames Water to task for tapping into residents outside London.

Over the past year Joseph Cass, 76, has lodged complaints about Affinity Water customers “subsidising Thames Water customers for their grandiose drainage schemes”.

He has taken issue over a substantial increase in the sewerage component of his water charges.

Affinity Water collects such charges on behalf of Thames Water, and Joseph’s bill for 2015/16 shows that while the water rate increased by 3.4 per cent, the wastewater component rose by about 14 per cent.

A breakdown of the latter shows a four per cent increase to help pay for the Thames tideway tunnel – the capital’s 25km ‘super sewer’ under London which, it is hoped, will tackle the millions of tonnes of sewage pouring into the River Thames each year.

The project has been criticised in the media for its £4.2 billion cost.

Joseph has written repeatedly to Affinity Water, Thames Water, water regulator Ofwat, the Competition & Markets Authority and St Albans MP Anne Main to complain about the “manipulation of the billing system”.

He told the Herts Advertiser: “It’s an injustice. My sewage is processed locally so I will not use the tunnel.”

But his enquiries have been “treated with disdain” by Affinity and Thames Water, with the former trying to push the pensioner, whose water is not metered, into “having a water meter installed”.

What has particularly irked Joseph is that Thames Water told him that its own household customers who receive both wastewater and water services saw total bill increases in the order of just one per cent, as an increase in wastewater prices was substantially offset by a reduction in water prices.

However, where Thames Water supplied the wastewater service, and the water was provided by the likes of an external organisation, such as Affinity Water, that was not the case.

Joseph believes there has been a “manipulation of costs by Thames Water…[which] makes other water companies subsidise their own customers. The whole issue looks to me to be creative accounting by Thames Water in order to meet a political goal of not increasing water charges by a large amount.”

A spokesman for Thames Water admitted that residents were paying an additional £20-25 for the Thames tideway tunnel project, with wastewater bills to remain at around the same level, before inflation, until 2020.

She said: “We carry out investment across our region when it is needed, with the cost always spread across the entire customer base. So any major work in Herts, for example, is paid for with help from people in London.”

An Affinity Water spokesman said: “Water charges for the five-year period have been agreed and approved by Ofwat.”

Mrs Main has contacted Thames Water to ask about the cross-subsidisation.