Fares will go up again on Sunday for some of the passengers using Bradford's biggest bus company - at the height of a drive to get people to use public transport.

First has put up most of its fares in four stages throughout the year instead of its normal block increases.

Sunday's final round of increases will put both 70p and £1 fares up by 5p and follows a rise 11 weeks ago when £1.05 fares went up to £1.10; £1.20 went up to £1.30; and £1.50 went up to £1.60.

In June, weekly First and Rider cards rose from £10 to £11; the company's monthly cards increased from £34 to £36, with annual tickets going up from £340 to £345 which, the company said, was the first price revision since 1999.

Today First came in for criticism over the increases and its failure to explain in detail why they were necessary.

Many people said they had been unaware of the latest round.

Today a First spokesman said: "Our costs are continually rising and we have to ensure that we don't run at a loss which may put the services at risk.

"To avoid block price increases we have staggered the increase to minimise the impact on customers and staff."

She admitted the majority of fares had increased but said it had been minimal and there had been leafleting and publicity on buses and at Bradford Interchange.

Councillor Ann Ozolins, of the West Yorkshire Passenger Transport Authority, said: "I believe these are price hikes by the back door. If they had all been put together people would have been outraged. It's a big and very unwelcome increase.

"There seems little point in Bradford Council making the provision of bus bays a condition of planning consent for things like shopping complexes when ticket prices are going up in this way.

"People in my ward aren't even satisfied with the services they are getting. They say there are too many buses on some routes and too few on others. I am asking for this whole issue to be put on the agenda of the PTA Bus Working Group."

Councillor John Prestage, chairman of Bradford Passenger Transport Consultative Committee, said: "I am very concerned over this.

"It is at a time when many, many measures are being taken to try to get people to stop driving and use public transport."

Councillor Dave Green, who regularly travels by bus, said: "If we don't get a reasonable explanation, all we can think is that the company is trying to bolster its profits.

"We have a Government which is committed to increasing the use of public transport. Off-peak fares are still reasonable but they are obviously aiming at people travelling peak time." Councillor Stanley King, leader of the Conservative group on West Yorkshire Passenger Transport Authority, said: "People need an explanation if they are going to be willing to pay it.

"First should give the reason as well as the increase - it's common sense to do so.

"In terms of PR it might have been better to put them all up at the same time.

"Unfortunately there's inevitably going to be some sort of annual increase."