We and others have had good results with South African Airline Cargo. See link below from the Shipping page on the reverse shipment to the one you are making.
Their website doesn't provide UK contact numbers, but a quick search on yell.com turned up this:
South African Airways Cargo
Buiding 557, Shoreham Rd West Heathrow Airport London
Hounslow Middlesex TW6 3RT
Business Type: CARGO HANDLING
Tel: 020 8897 0807
Please let us know how you get on.
Good luck and safe travels!
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