Since their earliest days museum collections have included human beings, as they provide evidence for subjects such as evolution, burial customs or disease.

But over the past few years, the retention by museums of human remains from the relatively recent past, and particularly of indigenous peoples, has come to be a focus for the very real anger that the descendants of those communities feel about the way their ancestors were treated.

Since the 2004 Human Tissue Act, national museums have been able to return human remains to their communities of origin. The British Museum (BM) has received two such requests since 2004: the first from Tasmania for two cremation ash bundles; the second from New Zealand for the return of nine bone fragments and seven preserved tattooed heads. The museum has agreed to the requests for the cremation bundles and the bone fragments.

When the BM's trustees consider these requests, they have to make a very difficult judgement about the strength of the case made by a community for return against their responsibility to preserve the collection for the benefit of other communities, both present and future.

To guide this complex discussion they take independent advice and follow the policy they developed in 2004, which excludes from repatriation any remains that have been modified into something else.

So, for instance, Maori fish hooks and flutes made from human bone are not eligible, and were not included in the New Zealand authority's request for return.

The museum's policy focuses on remains that were intended for burial (or other forms of mortuary disposal). If the trustees think it is likely that specimens were intended for burial, they then apply a "public benefit" test: whether the significance the human remains to the community making the claim outweighs the public benefit to the world community of retaining the human remains.

To reduce these complex issues to a few points: the Tasmanian cremation ash bundles and Maori bones were clearly intended for mortuary disposal. The status of the preserved heads is unclear; some were preserved as revered ancestors, but others were trophies of defeated enemies and others seem to have been produced for sale to Europeans.

So it's not clear they were all destined for mortuary disposal, or how one can distinguish between them. In addition, the heads provide rare insights into specific aspects of Maori culture, and their potential for future research is greater than that offered by the cremation ash and bones.

We welcome the chance to discuss these difficult matters but we also recognise that the retention of human specimens places obligations on us - to ensure they are not treated offensively or gratuitously, in the way they are kept, displayed or researched.

Andrew Burnett is the deputy director of the British Museum, London