Heathrow Airport

a couple of thoughts. first, based on what you want to do, I think you're seriously overpacking. For your Africa trip, if you bring the safari-type clothes sometimes called guide clothes, those will be sufficient and perfectly adequate for that trip. If you purchase the guide pants with the convertible legs, those can double as shorts which you can wear as city clothes. A couple of more dressy tops can get you by for the city clothes. IOW, don't worry about how you're dressed; the goal is travel light. As far as you thoughts of posting a suitcase to your hotel from Heathrow, you're going to have to go through customs and immigration at the airport in order to collect your luggage and then arrange to send it to wherever you're sending it to. I think that's unnecessary and time consuming. If you must have a different wardrobe, which I suggest you don't do, ship it directly from home. there are any number of services that will do that in a far more secure way than the way you are thinking of doing.

It appears that you're stuck. It probably would have been better to have requested some advice before you booked the trip, and possibly had taken two trips to eliminate the problem. I recall hearing ab out some company that did exactly what you want; shipped your clothes from home to be picked up when you arrived, but I don't recall its name. But an internet search will probably reveal not one, but any number of companies that will do what you want.

Maybe a long shot, but perhaps you could use the AirPortr service to have your bag delivered from Heathrow or Gatwick (they handle both) to your London hotel. I know they do that, but normally within the understanding that you will show up at that hotel sometime later that day to check in and collect your bag. However, if you could get the hotel to agree to store that suitcase until you arrive from Africa, albeit weeks later, then that might be possible. AirPortr puts plastic zip tie-type devices to secure a bag. And then that is supposed to be released upon delivery to the hotel. Even if the hotel agrees to do this, you'd have to be comfortable with how secure the bag would be in the hotel's luggage room. If it's a finer hotel, then maybe you'd have few worries.