Scotland's largest bus operator has increased its fares by up to 25%, only weeks after a cap on price rises was removed by the Competition Commission.

First Bus put up fares from Sunday, blaming an increase in costs, including fuel. Last month, it stated drivers' wages were also a factor in calling for permission to raise fares above the agreed rate.

The cost of an adult single will increase from between 80p and £2.80 to between 85p and £3.10. The child fare range will rise from between 45p and £1.20 to 55p-£1.35.

An all-day unaccompanied child ticket, which is popular with children travelling to school, will increase by 25% from £1.60 to £2, while a four-week two-zone FirstCard will rise 12%, from £23.10 to £26.

The Scottish Government will also face an increase in the amount of cash it pays under its free bus travel for pensioners scheme. Bus firms submit claims for the number of free passengers they carry.

First receives 73.6% of a standard adult fare for every free passenger, and the total will rise in line with the new fares. Uptake has been rising since it was introduced, with 113,000 pensioners and disabled people in the Glasgow area signing up.

Drivers, believed to be considering balloting for industrial action over a pay settlement, are angry that passengers are being asked to pay more, with increased wages given as one justification for the fares rise.

Passengers learned of the increases through leaflets and posters on buses on Sunday. A statement said: "From Sunday May 18, First in Glasgow will implement a revised fare structure across its greater Glasgow network. Our main single fares have increased by just 10p after many years, whereby bus fares in Glasgow have risen at a level below increases in bus industry costs including fuel.

"For regular travellers, some fares remain unchanged and our popular FirstWeek season ticket has risen from £12.50 to £13.50 after some 20 months when this price has not changed."

First yesterday declined the opportunity to add to the statement. However, the company's fares chart shows 13 adult single prices, all of which increase, and five child singles, all of which rise. Its adult FirstCard has 12 combinations of zones and timescales, all of which rise, as do the seven child versions. Only the accompanied child fare of £1 remains unchanged.

Last month, First was freed from long-standing undertakings that it would not increase fares by more than the retail price index. It argued that costs had increased disproportionately with the rest of Britain, with firms north of the border not receiving an increase in fuel duty allowance.

The Competition Commission agreed First Bus was not able to meet the rising costs as a result of the cap, as well as meeting the increased cost of wages, maintenance, insurance and fuel per year in line with the UK average.