The FTSE 100 company warned that commercial volumes continued to be hit by a large rise in unemployment in the North West of England in the last two years.
But United, which covers seven million people in the North West, posted a 4% increase in revenue to £822.9 million in the half year to September 30 as prices rose 5.8%.
The Cheshire-based group said underling pre-tax profit was up 3% to £190 million in the period as it invested £354 million in its network.
The company, which revamped its customer services last year after it received more complaints than any of its rivals in 2010/2011, said complaints had fallen a further 12% in the half year. It had no "escalated" complaints for the first time, it added.
Chief executive Steve Mogford said: "We are continuing to invest in our network for the benefit of our customers, the environment and the local economy."