For a few weeks only, visitors to Westminster Abbey can gaze on the second-last resting place of Oliver Cromwell, the grave which the Lord Protector occupied for less than three years before being dug up, ritually executed, decapitated, and buried again in quicklime at the foot of the gallows.

The stone slabs engraved in the 19th century with the name of Cromwell and his relatives are usually covered by a blue carpet bearing the RAF crest. Recently moths were discovered in the building's historic textiles. So the carpet has been lifted and sent off to be deep frozen to kill any grubs, leaving the chapel's extraordinary history exposed until the end of August.

"Few people come here following the trail of Oliver Cromwell, but this opportunity adds one more layer to the extraordinary richness of the history of this building," a spokeswoman said.

By the time he died of malarial fever in September 1658 aged 59, Cromwell ruled in such grandeur that many speculated he would soon be crowned king. Instead he was buried in the abbey in a tremendous ceremony modelled on the funeral of James I, in the same vault as his son-in-law Henry Ireton, one of those who signed the death warrant of Charles I, and John Bradshaw, president of the High Court at the trial.

The stone slab records simply "these [remains] were removed in 1661". In fact the three bodies were not only exhumed by order of Charles II within months of his restoration; they were hung, mutilated, and reburied at Tyburn like common criminals.

However, the unresolved mystery of Cromwell's bones did not end there.

According to one account, a daughter begged the body from the executioner, and had it secretly buried. Another version says the embalmed head was stuck on a spike outside Westminster Hall where the king was tried. A quarter century later it is said to have blown down in a violent storm, to be stolen by a sentry who only admitted this on his deathbed.

Arthur MacGregor, archaeologist and recently retired curator of the Ashmolean museum in Oxford, has tried to disentangle the competing claims.

In the 18th century a skull claimed as Cromwell's was displayed for money in London. Another was once in his museum ‑ which also has Cromwell's death mask ‑ but has vanished. Yet another, which he thinks was probably fake because the fractures suggest a spike smashed through from above rather than from inside an impaled skull, surfaced in the 1990s in a family collection in Kent.

The one with the best claim was examined at a meeting at the Society of Antiquaries of London in 1911, when it was said still to have part of a spike embedded in the bone. That skull was buried in 1960 in the courtyard of Cromwell's old college, Sidney Sussex at Cambridge, in an unmarked spot to dissuade ghoulish souvenir hunters.

By splendid irony, the unexpectedly available space in the vault at Westminster Abbey was soon filled ‑ with the bodies of a troop of illegitimate offspring of Charles II and their families, including the Earl of Doncaster, son of the king and his mistress Lucy Walter, and Charles Fitzroy, Duke of Cleveland and Southampton, his son by Barbara Villiers, the woman described by Bishop Burnet as "a woman of pleasure ... vastly expensive and consequently very covetous".