SEX offenders and rapists could lose the right to receive big reductions in jail terms in exchange for pleading guilty, The Times has learnt.

Sentences can be cut by up to a third in recognition of a guilty plea, but new guidelines are likely after an horrific case in which a couple raped a 12-week-old baby girl. In a rare move, Lord Goldsmith, the Attorney-General, is handling personally an appeal against their sentences before a five-judge panel led by Lord Phillips of Worth Matravers, the Lord Chief Justice.  
 
An original appeal last month was adjourned so that Lord Phillips and four other judges could hear the case tomorrow because of the ?fundamental questions? it raises.

Alan Webster, 40, and Tanya French, 19, raped a baby when baby-sitting and photographed the abuse. Webster, from Hatfield, Hertfordshire, was jailed for life in February after pleading guilty to rape, indecent assault and making indecent images of a child. But his tariff ? the minimum time to be served before he can be considered for release ? was set at six years by St Albans Crown Court. French was jailed for five years and given an extended period of licence of five years on the same charges.

The sentences prompted a campaign for tougher treatment of the worst offenders.

Tomorrow?s appeal hearing could lead to new guidelines in cases of rape and sexual assault and, in particular, a cut in the hefty sentence discounts of one third or more that offenders can win when they plead guilty.

The move comes as Lord Goldsmith, the Government?s most senior law officer, acquired wider powers to appeal against sentences in new middle-ranking sexual offences. The law officers have the power, in the most serious cases such as rape, to challenge sentences that they believe to be ?unduly lenient?.

But Fiona Mactaggart, a Home Officer Minister, laid an order in Parliament last month to widen the appeal powers of the Attorney-General to include offences under the Sexual Offences Act 2003, many of which involve children. The Act came into force in May 2004.

The offences include: sexual assault; sexual assault of a child or sexual activity with a child; causing a child to engage in sexual activity; meeting a child after grooming; arranging or facilitating child prostitution or pornography; causing or inciting prostutiton for gain; and trafficking for sexual exploitation.

The Attorney-General has powers under the Criminal Justice Act 1988 to refer ?unduly lenient? sentences to the Court of Appeal. Most of those involved have been tried in the Crown Court. But last month?s order, which applies to England, Wales and Northern Ireland, extends his powers to offences that can be tried before magistrates or in Crown Courts.

The Attorney-General is understood to be taking tomorrow?s appeal because of the exceptional nature of the crime and because of the wider principles involved and implications for future sentencing. He is also concerned that public confidence is maintained in the way that the courts tackle sex offences, because only a small proportion of rape cases end in a conviction.

The Attorney-General will be aware that any reduction in the discount given for an early guilty plea could increase the number of defendants who plead not guilty. In rape cases the impact would be small, as often a conviction hangs on the issue of consent and men accused of rape are more likely to plead not guilty, knowing that it is their word against that of the alleged victim.

But smaller discounts could have a wider impact on guilty pleas in other offences, which, in turn, might add to pressure on overburdened prisons.