At a conference on Wednesday, Prof Robin Lovell-Badge of the Francis Crick Institute and Dr Simon Fishel, head of the CARE fertility Group, are expected to propose that the research time frame should be extended to 28 days.
The move comes following recent scientific advances that have allowed researchers to extend the time embryos can be kept alive in the laboratory.
Dr Anthony McCarthy, of Society for the Protection of Unborn Children, said: "In 1984 the Warnock Report on embryo experimentation refused to examine closely when personhood began. Instead it came up with an arbitrary 14 day limit after which the destruction of new human embryos would be, not just permitted, but enforced.
"Now others who are similarly uninterested in fundamental questions concerning the rights of new human persons wish to expand the scope to create, keep and destroy those persons. That they wish to do so, in part, to help avoid miscarriage is morally obtuse."
Proponents of the motion suggest that by extending the experimentation period, more can be understood about human health.
Cancer and heart disease are among the conditions that some researchers say they can understand better through extended experimentation.
Baroness Mary Warnock, who originally proposed the 14 day limit in 1984, will speak at the conference in defence of maintaining the current experimentation period.
Lord George Carey, the former Archbishop of Canterbury, will speak about religious standpoint on embryonic experimentation.