Casualty 8.50pm, BBC One “We might be about to re-enter hell.” Holby continues to ramp up the drama with another 12-part series – entitled Lethal Legacy – which this time follows a mysterious illness that might start another potential pandemic. If that doesn’t sound too traumatic, the team have personal demons to face, too. Hollie Richardson Secret Africa: Into the Wild 7pm, Channel 4 Explorer Lucy Shepherd continues her survivalist trek through some of the remotest parts of Tanzania. She and local guides must reach a resupply point before tackling the Serengeti. Obstacles include curious elephants, killer bees and some unfortunate digestive issues. Graeme Virtue Black British Music at the BBC: Volume 2 8.50pm, BBC Two Diamonds are forever … Black British Music at the BBC: Volume 2 on BBC Two.…