Online ticketing business Trainline sunk to a heavy loss as executives revealed it cost £21 million to list the company on the London Stock Exchange.

The company saw pretax losses grow from £11 million last year to £89 million in the six months to August 31, although stripping out one-off costs, pretax profits were £42 million, up from £21 million during the same period last year.

Trainline employs more than 600 people across its offices in Edinburgh, London and Paris.

Net ticket sales rose 19% to £1.8 billion with executives saying this was due to an increase in customers using its website and app together, and more train users willing to switch to etickets.

READ MORE: Rail app firm's sales jump 20% since floating

Revenues increased 29% to £129 million and the company said it will turn its attentions to growing its business division, selling train tickets direct to companies.

In June, Trainline announced a revenues upgrade as sales were proving greater than previously expected.

READ MORE: Trainline shares surge on £1.7bn stock market debut

However, the cost of bringing Trainline to market took its toll. A further £70 million one-off charge was taken in relation to finance costs.

Chief executive Clare Gilmartin said: "We continue to focus on making rail and coach travel easier for customers worldwide, thereby encouraging a much greener way to travel.

"As most rail and coach tickets continue to be sold offline at the station, and as customers and governments commit to more environmentally friendly modes of travel, we see significant growth opportunities for Trainline over the long term."