Thanks all for the information. Originally I was a bit miffed when our TA opted for ex LGW rather than ex LHR for our trip to South Africa in August, but over time I found out;

1. We're on a 380,
2. As there are four of us travelling together in J the CDC company is happy to go over the 70 mile limit to pick us up / return us home,
3. There's the dedicated CDC drop off (not VS DTCI, but close enough...)

and now positive reviews of the lounge. All that remains is the look on on our offsprings' faces when they realise we're travelling J class.