The Archbishop of Canterbury and York will embark on a "walk of witness" in March, to express repentance for the Church of England's complicity in the slave trade.

Carrying a giant cross through London, the Archbishops of Canterbury and York are to lead thousands in a march, while moments of quiet reflection will be held as African drummers beat a sombre lament.

The event, which takes place on March 24, coincides with the bicentenary of the abolition of the slave trade. It is the latest stage in the Church's commemorations since February last year, when the General Synod voted to apologise for its involvement in slavery.

The vote at Synod was supported by the Archbishop of Canterbury Dr Rowan Williams and the Archbishop of York Dr John Sentamu, who has linked slavery with modern-day discrimination and racism.

Churches across Britain are being encouraged to bus up to 8,000 parishioners to London for the "act of public witness", according to draft plans.

Rowan Williams, the Archbishop of Canterbury, and John Sentamu, the Archbishop of York, who grew up in Uganda and has described how his forebears were among those enslaved, hope the event will signal the "beginning of a healing process".

The march is understood to be taking two separate routes through the capital, meeting at Kennington Park in south London for an open-air church service. The Archbishops are expected to march alongside a group of black and white youths bearing the cross.

Before leaving Whitehall, the Archbishops will take part in an act of reflection. They will then walk past the Houses of Parliament, pause for remembrance prayers at Victoria Tower Gardens, and proceed to Lambeth Bridge. From this point, the marchers, excluding the African drummers and a small group of singers, will fall into silence.

The route across the Thames has been chosen to represent the Atlantic crossing made by more than 10m Africans sent to the Americas between the 15th and early 19th centuries.

The symbolic "release from the past" is to be the climax of the service, likely to be followed by a "song of freedom". Worshippers will be then asked to sign a petition calling on the government to take action against modern-day slavery, such as sex trafficking from eastern Europe.