After one of Westcott’s students approached him for pastoral support, he gave her his mobile phone number and began to send flirtatious messages, despite being married.
soon turned intimate, as the couple began to have consensual sex.
The girl was 16 and taking her GCSE’s (in Year 11) at the time, before joining the school’s sixth form.
According to Swindon Crown Court, she even babysat Westcott’s children and became a “friend” of his (now ex) wife Deborah.
Their affair first came to light when the National Society for the Prevention of Cruelty to Children (NSPCC) received an anonymous phone call.
Following an earlier hearing at Chippenham Magistrates' Court last month, Westcott admitted to three charges of sexual activity while in a position of trust.
After the hearing in Chippenham, Westcott, who had only been suspended from his job following his arrest in October, was evidently sacked.
The head of the school - which cannot be named for legal reasons - said
: "The school was required by the police not to initiate internal investigations until police investigations were complete.
Following the court proceedings, the school has terminated Mr Westcott's employment with immediate effect.
"You will appreciate that for confidentiality reasons, I am unable to provide further details, but would like to assure you that those involved in this matter are being provided with appropriate levels of pastoral support."
At the most recent hearing at Swindon Crown Court, Charles Row, defending, said
: "[Mark] has let so many people down, himself, his family and the teaching profession."