ferret on Family Tree Circles

I am trying to trace my great grandfather (Alexander LAWRENCE). Details I have been given from the book "Aided Immigration from Britain to South Africa 1857-1867" by Esm? Bull are:-

Permit No........R1520/P1397
Name.............Alexander LAWRENCE
Age..............22
Status...........Single
Occupation.......Labourer
Destination .....1 Chapel Street, Cape Town. South Africa.
(Residence of Brown LAWRENCE)
From.............County Derry, Ireland
Ship............."John Vanner"
Departed from....Southampton on 4 January 1862
Arrived at ......Table Bay, Cape of Good Hope on 10 March 1862
Travelled with...Mary LAWRENCE aged 20, single.

I understand he was born on 23 February 1840 in Coleraine, Londonderry, and was the son of an absentee English landlord.

I am hoping someone will be able to help me:-
a. Trace him back to Ireland.
b. Establish who his family was and whether they were English or Irish.

Thanks for any help.
ferret