Women in their early 20s should be screened for cervical cancer, a study has said.
Rates of cervical cancer have fallen since screening began
Under-25s have been excluded from such checks in England since 2004 because of relatively few cancers being detected, and concerns about invasive treatments.
But researchers in the Journal of Family Planning and Reproductive Health Care say this may put them at a higher risk of developing cancer.
However, an NHS Screening Programme spokeswoman rejected the proposal.
Smear tests detect pre-cancerous changes called CINs, as well as cancers themselves.
This study, by a team from Guy's and St Thomas' NHS Trust in London, says the incidence of CIN3, the highest grade, is increasing in younger women.
Those aged 20-24 made up 19.3% of all cases of CIN3 in 2004, compared with 15.8% of all cases in 1999.
More recent figures are not yet available but the team, led by Dr Amanda Herbert, say trends such as earlier sexual activity mean the incidence is likely to have increased further.
The study says women aged 25-30 are also being affected.
The proportion in that age group coming in for smear tests fell from 80% in 1995 to 70% in 2005/6, meaning cases are often picked up only when the disease is more advanced.
Dr Herbert said: "It would probably be OK if women all turned up at 25, but they don't. They may not be getting the message that it's important for them to have smears when invited.
"And in the past, they were given information about having smears at school or college. Now those opportunities are being missed."
Reinstating early screening would mean that pre-cancerous changes could be detected much earlier and monitored closely, and that women could be advised that stopping smoking and practising safer sex could reduce their risk of developing cancer, the researchers say.
Women in Scotland, Wales and Northern Ireland are still called in for smears from the age of 20.
Professor John Shepherd, a cervical cancer specialist and spokesman for the Royal College of Obstetricians and Gynaecologists, said younger women should be screened.
"Ten per cent of those with cervical cancer - around 200 women a year - are aged 30 or under.
"If those women had been screened from 20, or from when they began having sex, they may have been detected earlier."
But Julietta Patnick, director of the NHS Cancer Screening Programmes, said cervical screening in the UK adhered to International Agency for Research on Cancer guidelines, which say women under 25 should not have smears.
She added: "Cervical cancer in under-25s is extremely rare, but changes in the cervix are common.
"This can result in unnecessary invasive interventions and treatments, which can result in unwarranted anxiety and potential complications."