Rather worrying article here from M&G:
Passengers in transit to London must ensure that they comply with new security measures on hand luggage, South African Airways (SAA) said on Friday.

The airline said in a statement that passengers connecting to further destinations are requested to travel without hand luggage to avoid inconvenience at London's Heathrow airport.

--and--

As stipulated by the British government, all flights departing from London will be subjected to full security screening.

Passengers will be hand-searched, their shoes will be removed and they will be X-rayed. Pushchairs and walking aids will also be checked and screened. Only essential items will be allowed in hand luggage for flights departing from London.

Pocket-sized wallets and purses, essential medication marked with the passenger's name, unboxed tissues and female hygiene products and unboxed spectacles will be allowed. All other items will have to be placed in the hold.

No electrical or battery-powered items such as laptops, cellphones, iPods and remote controls will be allowed in the cabin and must be checked in as hold baggage.
Can laptops take travelling in the cargo hold?

And what about JHB International's baggage pilfering problem?