A married mother who was spared jail for having sex with a 'vulnerable' teenage schoolboy is tonight starting a two-and-a-half year jail term - after top judges ruled her original punishment was 'too soft'.

Kelly Jane Richards started a relationship with the 15-year-old which eventually led to the pair having sex, after which she told him: 'Don't tell anyone because I might get done for this.'

The 36-year-old mother of two, of Mountain Ash, Rhondda Cynon Taf, admitted engaging in sexual activity with a child at Merthyr Tydfil Crown Court in March.

Kelly Jane Richards, 36, is tonight starting a two-and-a-half year jail term after her suspended sentence for grooming a 15-year-old boy was overturned by the Court of Criminal Appeal in London as it was too 'lenient'

She was handed a two-year suspended sentence and a sexual offences prevention order, after the crown court judge decided to show her 'mercy'.

But she was today given a two-and-a half year jail term by judges sitting at London's Criminal Appeal Court, who said the initial sentence was 'unduly lenient.

Richards, whose husband has stood by her, was ordered to hand herself in at Merthyr Tydfil police station by 4.30pm today.

The court heard she started a relationship with the teenager, regularly contacting him on his mobile phone and through Facebook and Twitter, in 2012.

When the boy's mother became concerned about his 'secretive' behaviour and confiscated his mobile phone, Richards bought him a sim card so they could remain in touch.

Their illicit relationship was discovered after the mother grew more suspicious and recorded one of their phone conversations.

She went to the police and the boy, who was described as being 'particularly vulnerable', eventually told officers what had happened.

He said she had 'treated him like an adult', occasionally giving him alcohol and once asking him to give her a massage, before they had sex.

The boy had also told friends he was in a relationship with an older woman and that she was going to leave her husband for him.

The Court of Criminal Appeal ruled that Richards had been 'sexually provocative' with the teenager

Lord Justice Davis told the court that, while Richards behaviour might not have been 'grooming' in the usual sense of the word, her actions towards the teenager were 'sexually provocative' in the weeks before and after they had sex.

She had also tried to disuade him from telling anyone and there was a big age gap between the pair.

The judge said the offending could not be described as a 'moment of madness', adding: 'No doubt what happened was not planned and was impulsive.

'But it was, in effect, the culmination of sexual conduct which had been provocative in its nature, so far as Richards was concerned.'

Lawyers representing the Attorney General, Jeremy Wright QC, argued that, in light of all these factors, the crown court judge should have imposed a stiffer sentence.

Richards' lawyers said the judge had showed a degree of mercy, taking account of the fact she is the mother of two children and suffers anxiety and depression.

They also argued she had made good progress with the probation service in the months since her sentence was passed, and said that a term of imprisonment may result in her family losing their home.

But, jailing Richards, Lord Justice Davis said that, even taking into account all of the mitigating features, her original sentence was 'unduly lenient'.

Sitting with Mr Justice William Davis and Judge Nicholas Cooke QC, he added: 'This was a serious case of its kind, not least because of the very troubling elements of sexually-charged conduct of the offender before and after the sexual activity took place.

'Moreover, it has to be noted that her behaviour and her conduct have had a profound effect on the boy himself.