The text below is from the Liturgy Commission of Westminster Diocese (2008)
The comments below were given a more definitive ruling in 2016 by a Vatican instruction forbidding the scattering of ashes, see here
Because Christians do not believe that death is the end of the human person, and we do believe in the resurrection of the body, we show care and reverence for the mortal remains for those who have gone before us marked with the sign of faith. “Since in baptism the body was marked with the seal of the Trinity and became the temple of the Holy Spirit, Christians respect and honour the bodies of the dead and the places where they rest.”(Order of Christian Funerals ,19)
Our tradition is to bury the mortal remains of the dead, entrusting them to God until that day when they are raised to the glory of new life. For centuries the practice was for the body of the deceased to be interred directly. More recently cremation of the body has become a general practice, largely for environmental and economic reasons.
The Church used not to permit cremation. This was largely because enemies of the Church sometimes imposed cremation of the bodies of the faithful and the scattering of their ashes. This was in order to try to ridicule the Church’s belief in the resurrection, or as a way of seeking to obliterate the memory of Catholic martyrs.
More recently the Church has permitted cremation. The former reasons for objecting to it do not generally apply, and there are often good environmental and social reasons for preferring cremation.
However cremation is not the same as burial. Cremation merely speeds up what would be the natural processes of disintegration of the mortal remains after death. When cremation has been completed, the ashes remain. These ashes are mortal remains. They should be reverently interred as soon as possible – as a sign of our continued care and reverence for the deceased, and our trust and expectation that God in his mercy will raise the dead to new life.
Burial of Ashes
The Church provides a simple rite for the burial of ashes.
There is no set time by which the ashes must be interred, but it is best that the ashes be buried sooner rather than later, if only for the sake of reverence for the mortal remains of the deceased.
It is usual to ask the priest to lead the service for the burial of the ashes, but the service can in fact be lead by anyone. If you would like someone else (for example a member of the family) to lead the service, your priest can provide you with a copy of the rite and the prayers
Place of burial
There is no particular place where the Church requires cremated remains to be buried. However it is most common for ashes to be interred in a dedicated cemetery or in a memorial garden. Your funeral director will be able to offer guidance as to what burial grounds are available locally.
Where ever ashes are buried it is intended by both Church and State that those ashes will remain there. Indeed, by law, once they have been buried cremated remains may not be removed without permission from the Home Office, and in some circumstances from the Church also.
A 2016 document from the Congregation for the Doctrine of the Faith commented on some recent secular trends, including New Age ideas that death is a “fusion” with Mother Nature and the universe, or the “definitive liberation” from the prison of the body, and noted:
Ashes should not be scattered (in the air, land or sea) as this can give the appearance of “pantheism, naturalism or nihilism”, that the dead disperse into nothingness
Neither should ashes be divided up, kept at home, divided up, put into lockets, jewellery, or other ‘mementos’.