What ingredients? Africa is a continent - do you mean Egyptian ingedients, Mali, Congo, South Africa???
There is a South African shop in the passage under Charing Cross station
If you're in London, it's not much of a problem there are large African Communities all over the place. The Stroud Green Road in Finsbury Park would be one place to look. If you're outside London, try ringing these guys they might do mail order, Stella African Food Shop,154 Rye Lane, London, SE15 4NB, Tel: 020 7639 9505.
Some of the street markets in areas known for having a multi ethnic population in all the big UK cities are worth a visit to make sure you get the freshest and most fairly priced food. You'll get plenty of advice on what to do with them when you've bought them if you need it too.