My experience in case it helps anyone else:

After a fair bit of walking from one of the further/outer arrival gates, the concourse splits into 2 sections in the 'main' section of the terminal- one for arrivals and one for flight connections. I decided to try flight connections and then double back if the queue was horrendous (which is what the VS guy I spoke to previously mentioned). It was only a 2-3 minute walk from the split to get to FC.

At 7.30am, flight connections was quite efficient with 3-4 stations open and the queue took only about 7-8 minutes to get through. It consisted solely of the security check (no passport or boarding passes, which is different from T5FC where you go through the passport/flight check first and thereafter merge with the regular security lines - which all adds to the time taken to clear).

You come out in the departures section at the far end of the terminal (airline transfer desks - the other end of the terminal from where the UC Private Secuirty Channel is) and it's a quick walk (less than 5 minutes) to the VS lounge from there.