A state-of-the-art prison, built by the United Nations to hold Afghanistan’s drugs barons, is being used to house ordinary prisoners awaiting execution.

The decision to move death-row convicts into the new U-10 wing of Policharki prison in Kabul, which has lain empty for 20 months, has caused acute embarrassment to the UK government, which opposes the death penalty and contributed about $2m (€1.3m, £1m) to the scheme.