Dozens of extra buses on London's roads helped FirstGroup please the City with a small rise in half-year profits, as the company increased services in preparation for mayor Ken Livingstone's congestion charge.

FirstGroup benefited from £13m of extra business running buses in the capital, which helped offset lower subsidies on its inter-city rail routes.

The company's operating profit increased by 1% to £84.4m, sending the shares up 10p to 231p. FirstGroup, which is the country's biggest bus operator, saw its profits from buses rise 5.5% to £45.9m, following a 1.5% increase in passengers.

Moir Lockhead, chief executive, said London delivered much of the rise, although he admitted he did not know whether services would be able to cope with an influx of extra commuters discouraged from driving by next year's £5-a-day road charge.

"No one can quite work out what demand is likely to be," he said. "If the demand is greater than we expect, we can always put on even more services."

The group's three rail franchises, which carry 280,000 passengers a day, turned in flat profits of £29.5m, despite a sharp reduction in subsidies from the government.