I wouldn't use autoglym SRP on any dark coloured car. If you do, it'll fill any scratches & stone chips with bright white, and I find also lightens the colour of the whole car slightly. If you have a light colour, then great, but i'm after an inky black finish to my cars which are both very dark coloured.
I tried a small amount of the Autoglym Wax when at a friends on Saturday. Didn't use much, as it seemed to "powder" really quickly.
My method of cleaning.
1. Take car to local trusted "hand car wash". They will spray it with a traffic film remover, and get the worst of the rubbish off.
2. Once home, clay the car using Meguiars or whoever's kit. The kits usually have clay, "detail spray" as a lubricant for the clay, and a micro fibre. Take your time and you'll see and feel the improvement in the paint. Don't drop the clay on the floor and re-use. That'd be very bad.
3. Unless paint is very swirled, I then apply a layer of wax. I'm a Zymol fan. Not cheap, but its easy to use & quick.
4. From there on, wash the car yourself, using two buckets & grit guards if possible. Further applications of wax can be applied as & when.
5. NEVER return to the hand car wash. They will scratch your paint.
I did the above on Saturday, having just bought the S3, which lived in the middle of deepest rural farmland. It now looks very presentable, and the water beads really well.