BUS drivers in East Lancashire will be required to "sweep" their buses in future, after a toddler climbed onto a bus and spent four hours on board unnoticed.

Transdev Lancashire United launched an investigation after three-year-old Lee Loram got onto the 225 bus in Blackburn at 12.10pm on Friday.

After bosses studied CCTV footage, it has now been revealed that he travelled to Clitheroe and back to Blackburn before continuing to Bolton and back - a round trip of almost 50 miles - without anyone noticing, despite the 50-capacity bus being mostly full.

Lee's mum Kelly Stockman, 32, of Roe Lee is calling for a radio "alert" system to be installed on all buses so that parents will not have to go through the hours of desperate worry she and Lee's father Neville Loram - a bus driver for Transdev - went through when the tot went missing.

Lee was with Ms Stockman in Blackburn Market on Friday lunchtime when he climbed onto the bus in Penny Street when his mum's back was turned.

His disappearance sparked a major police search, with a police helicopter deployed and officers drafted in from across Lancashire during the four hours he was missing.

CCTV footage from the bus shows that it is only when two girls from Darwen Vale High School spotted Lee on his own at around 3.45pm that the driver realised he was on board, on the way back to Blackburn.

The driver handed Lee over to police and Mr Loram as soon as the bus arrived at the Boulevard.

John Threlfall, operations director at Transdev's depot in Intack, said: "We have analysed the CCTV from the bus, shot from the front above the driver's head, and you can see the young lad get on and confidently walk down and hop onto the back seat.

"But it is clear that the top of his head would only have been just visible in the rear view mirror, and bus drivers rarely look in that mirror.

"They use the side mirrors to navigate and usually only glance in the rear view to see if people are getting off or on."

He said it looked likely that Lee had gone to sleep during the journey, and was brought to the driver's attention by two girls on their way home from school.

The youngster was brought to sit behind the driver, who spoke to him to make sure he was OK, for the last bit of the journey.

Mr Threlfall said the 225 route does not normally include a stop of more than a few minutes.

"It's a semi-circular route so at both ends, in Clitheroe and Bolton, it runs round the bus stations without a complete stop. I believe that the service was also running a little late because of Friday traffic, and the law states you cannot be more than five minutes late, so the driver would not have stopped for any longer than necessary.

" But this was obviously a regrettable incident and the driver, like everybody, is glad that no harm cam to the lad, but we need to do something to address it."

As a result of the incident, Transdev will be asking all its drivers to do a brief walk of their bus at the end of routes to check for any children or anybody else in any kind of distress, he said.