A social worker assigned to the family of Tania Clarence, who killed her three disabled children earlier this year, was unexpectedly replaced amid fears she was getting too close, a court has heard.

Forensic psychiatric Philip Joseph told the Old Bailey today Kingston Council's decision to switch Tania Clarence's social worker was "an important trigger" before the killings. The replacement, he said, was "a real novice".

Clarence, 43, of Thetford Road, New Malden, killed twins Ben and Max, three, and Olivia, four, in April, by smothering them as they slept.

Murder charges against her were dropped last month, with the prosecution accepting her plea of manslaughter on the grounds of diminished responsibility.

Clarence, who was not present when the murder charges were dropped, was overcome with emotion and had to leave today's hearing after less than half an hour.

At the hearing prosecutor Zoe Johnson QC said a social worker from Kingston Council was replaced because her bosses feared she was getting too close to Mrs Clarence.

The social worker was experienced in working with under-fives and had a "reasonably good working relationship" with the family, Miss Johnson told the court.

Bosses feared she was too close to Mrs Clarence, she said, adding the replacement had joined the council only six months earlier.

The reaction of the original social worker was to resign.

Miss Johnson said it was "perhaps an ill-conceived decision" to have replaced her.

The court was told of the Clarences' often fraught relationship with medical and social workers over surgical intervention for the children.

The professionals’ concern went so far that legal proceedings against the Clarences were considered.

The couple stuck to their belief that their children's quality of life was more important than their longevity, but were at odds with doctors and others who defence barrister Jeff Sturman QC said did not take a "joined-up" approach to the care of all three children.

About 60 professionals, all told, were allocated to the family and often visited unannounced.

Mr Sturman said medical professionals were "all wanting to be taken first, all wanting [Clarence] to bring the children to them, very few of whom were willing to come to the house" for appointments.

Mr Clarence said in a statement: "Despite my best efforts and constant pleading with medical professionals to minimise interventions, I was not able to get them to modify their approach."

Mr Sturman said Clarence tried to make the home a "refuge" from medical treatment. He added: "It is quite understandable that this mother wanted her children to live as normal a life as possible."

He added that due to the volume of their treatment the children were scared of medical workers. Olivia developed "phobic tendencies", he said, and Ben sometimes vomited from fear.

All three hated the machine Clarence learned to use at home to suction fluid from their chests at night, Mr Sturman said.

He added Clarence "could not bear to see the children in pain", as often occurred during physiotherapy sessions.

The court was told that if the Clarences had known of their twins' disability - they, in common with Olivia, had spinal muscular atrophy - they would have aborted the pregnancy.

Ben and Max were born prematurely during a family holiday to Portugal in July 2010, and had to undergo surgery and blood transfusions.

Originally from South Africa, the Clarence family moved to New Malden from Wimbledon last year.

When police arrived at the Clarences' house, on April 22, they found a note in Clarence's en suite bathroom, written in English to her husband.

It read: "Gary, I couldn't live with what I've done. I took tablets but they didn't work. Please don't save me. Love you."

Clarence also wrote a heartrending letter to a beloved nanny who had looked after them for years.

In the letter, which she handed to the nanny on the night of the killings, she apologised for what she had done and thanked the nanny for her "amazing" help.

She wrote: "I'm so sorry I had to do this but I couldn't carry on.

"I also couldn't leave the children with [her husband] Gary - it would have been too much for him.

"You have been the most amazing person in our lives over the last few years.

"Please believe me when I say that you did far too much as is."

Miss Johnson told the court this morning the nanny had been a "valued and loved member of that family" for four years.

The court also heard tributes from teachers to the children.

Ben and Max were described as "chatty, full of smiles with a real sense of fun".

They were "eager for new experiences," Miss Johnson said.

Olivia was "unwaveringly cheerful and positive" and "very matter of fact about her disability," she added.

Olivia "loved dinosaurs and she loved dressing up as a princess," she said.

Mrs Clarence enjoyed a good relationship with Alexandra Infants School, Miss Johnson said.

Olivia was taken for an introductory visit on June 21, 2013. Once she started there "she settled in quickly and enjoyed her schooling", Miss Johnson said.

She added: "She soon developed as a leader among her friends.

"Everyone wanted to be her friend.

"Her attendance was just over 70 per cent which is extremely good considering how many hospital appointments she had."

Olivia looked forward to her brothers joining her at school in September this year, Miss Johnson said.

Mr Justice Sweeney will sentence Clarence on Tuesday.