Helen Murray, 38, from Dobson Walk, Corby, Northamptonshire, denies one charge of driving without due care and attention at Northampton Magistrates' Court.

Murray was driving a Ford Ka when it was involved in the crash on the A427 in Corby on April 28 last year.

Her son Luke Murray and his friend Terence McMahon, both 13, were both killed in the crash along with Luke's six-month old German shepherd puppy Remus.

Today Sarah Brooks, prosecuting, told the court Murray had pulled across the road to turn right into the path of an oncoming van driven by Alan Scales.

She said: "This is a very tragic collision.

"Mr Scales has come from Market Harborough along that road.

"He approaches the junction and as he does so a Ford Ka motor vehicle comes across the front of his Transit. He can't avoid the collision.

"As a result he strikes the motor vehicle and of course there are then tragic consequences as a result of that."

Murray bowed her head and wept as the case was opened to a packed public gallery.

Miss Brooks said an independent witness saw Murray pull straight across the carriageway in one manoeuvre, without stopping.

She said: "She should have seen oncoming traffic, she failed to do so and failed to act appropriately in the circumstances.

"A competent careful driver exercising all care in the circumstances would have seen the oncoming vehicle and would have acted accordingly.

"The competent and careful driver would have remained at the right turn arrow and waited until the Transit had gone away.

"We are not suggesting anything more on the part of Mrs Murray other than inattention."

Mr Scales said he could not have avoided the crash.

He told the court he had been returning from a trip to Market Harborough where he had been practising on his motocross bike.

He said he had driven the route hundreds of times, as he used to be a lorry driver.

Mr Scales said a Renault Megane Scenic in front of him had pulled into the slip road to turn left, then he had suddenly seen the Ford Ka cut across the road.

He said: "The Renault pulled down the slip road, I went past and then I was confronted with a Ford Ka in the middle of the road, side on to me.

"I tried to swerve into the middle of the road to get round the back of the car but I was just too close, there was nothing I could do.

"I can't remember it coming down the filter lane in the middle, I just remember seeing the car in front of me and thinking 'oh my god' then the next thing I remember is swerving down the road.

"There's nothing anybody could have done, it was too close."

Mr Scales told the court he had to climb out of his van further down the road, where it had ended up on its side.

Rob Bimpson, defending, said Mr Scales had overtaken two vehicles earlier on, before the collision, and suggested he had been rushing for some reason.

He also said it was possible Mr Scales had moved into the middle of the road to move round the car slowing down, and that was why Murray had not seen him.

Mr Scales said: "It did not feel like I was going that fast, I honestly don't know how fast I was going.

"I was in my correct lane for the direction I was travelling."

Witness Tim Carey, who had been on a family outing to East Carlton Country Park near the scene of the crash, described the accident.

He had pulled on to the main road in his Renault Megane Scenic, only to travel a few hundred yards then turn left on to the slip road, he said.

He said he had seen the Ford Ka preparing to turn right.

He said: "It did not seem to be driving anything out of the ordinary.

"The car was driven as you would expect it to be. The indicator was on, signalling to turn right.

"It made the move in one manoeuvre, it did not come to a complete stop.

"As the car turned right down the road over my right shoulder came a transit van.

"The Ford was hit on the side, I saw a body fly out of the car, debris was smashed into the air all around. The car spun around."

He said the van did not appear to be doing anything out of the ordinary and had been driving in its own lane.

Another witness Agnes King described not seeing anything, only hearing the "awful" bang of the collision.

Pc Gary Wood, from Northamptonshire Police's Collision Investigation Unit, said he had carried out an investigation into the crash.

He said the van had been on the correct side of the road and said there was no indication it had crossed into the central hatchmarks.

Investigations showed the minimum the transit van could have been travelling was 48mph - the speed at the point of collision.

Mr Bimpson suggested to Pc Wood that it could have been travelling as fast as 65mph - over the 50mph speed limit - and that two other witnesses reported being overtaken by him earlier in his journey.

He said: "We can't divorce Mr Scales' driving from this tragic accident and you seem to be telling this court that it was perfect."