I got lucky with almost non existent queues; I arrived at 05:00. Although it's easy to see that on a busy day or at a more peak time it could take a great deal of time!

1: Passport check required to proceed from the first 'lobby' of the airport. Took no time at all.
2: Bag x-ray immediately after he passport check, including taking off jackets. 10 minutes.
3: I had no checked baggage so proceeded past the BA queues (which looked like they'd take about 20 minutes in the standard line) to the next passport check. No waiting time and collected my pink departures card here to fill out on the tables behind.
4: Short but slow queue for immigration. Took about 30 minutes.
5: Getting into the LAT lounge required the desk agent to make a phone call since I only had a mobile boarding pass. Once I got bored of being in there (which didn't take long as it's quite naff) I headed for gate 12 via the security check. This took about 10 minutes as there were hardly any people.
6: Arrived at gate 12 about 6:30 and it took 20 minutes to get through the bag search and I'm now in the holding pen.

Thanks for all the advice which enabled me to use the best entrances and minimise the walking!