National Express remained on track to meet annual expectations as revenue grew across the board in the first four months of 2015, the transport services operator said on Wednesday.

Group revenue rose 4% on a constant currency basis, while passenger volumes climbed 2% across the group's divisions and headline profit was higher than in the corresponding period in 2014.

The FTSE 250 group said its businesses in the UK were on a steady footing, driven by rising passenger demand and cost controls in the division, while its c2c rail franchise had started well, as passenger volume grew 4% and revenue jumped 10% following strong peak and off-peak travel.

National Express said revenue in its Spanish division grew 4% in the four months to April as passenger volume rose 7% in the region, while revenue in Morocco surged 17%.

Meanwhile, the group's operations in the US saw contract retention of 99% and average price increases of 5%, compared with 98% and 2% last year.

"We have made a good start to 2015 and are on track to deliver the board's expectations for the full year," said group executive Dean Finch.

"We continue to drive our strategy to develop opportunities in existing and new markets with a number of exciting bids submitted since the start of the year and our plans for further bids are progressing well."