According to [Timatic][1] you don't need a transit visa:

> TWOV (Transit Without Visa):

> Visa required, except for Holders of onward tickets for a max. transit time of 24 hours. 

However:

> 
>  Angola (AO)

> Vaccination against yellow fever required.

> Exempt from Yellow Fever vaccination:

> - Children under 1 year of age.
> - Passengers transiting Angola who do not leave the aircraft and continue their journey by the same aircraft.


[1]: https://www.timaticweb.com/cgi-bin/tim_client.cgi?SpecData=1&VISA=1&HEALTH=1&NA=GB&AR=00&PASSTYPES=PASS&DE=NA&EM=MA&TR=AO&VT=00&user=STAR&subuser=STARB2C