The firm supplies water to about eight million customers

It has blamed higher pensions charges and the weak US dollar for the decrease in pre-tax profits to �141.3m during the six months to 30 September.

The pensions bill of �15.1m offset higher revenues from the Midlands-based company's core water business.

The firm will learn on Thursday whether the regulator Ofwat will allow it to put up household bills by an average of �57 over the next five years.

It wants them to increase from �210 to �267 between 2005 and 2010.

Ofwat has already indicated that it does not accept certain parts of Severn Trent's business plan.

In the core water business, which serves about eight million customers between the Bristol Channel and the Humber, Severn Trent said price increases drove a 5.8% rise in turnover to �505.7m.

Its Biffa waste management arm was boosted by the acquisition of rival Hales in June.