Well, I have it for two months and can't share durability info. The impressions in these two months:

Good:
- Fast paced (4700MQ, a Crucial SSD)
- If I only work on the SSD file system, the HDD (7200rpm) goes into power-safe mode after a few minutes and I can't hear the notebook anymore (room temperature 20°C), else there is a slight, high frequency sound.
- Good, fast support (got it malformatted to do MS and after it got picked up, it got back to me in 2 days - don't know if this gets handled in the UK)
- Keyboard is better like e..g. on an Acer on which I had to type occasionally.
- USB3.0 works as expected and uses the HDD's full speed.
- Brightness is good (but okay, it's winter, haven't tested it outside).
- Pretty maintainable (occasional internal cleaning even recommended by Schenker)

Neutral:
- Screen is kind of stiff (less than 0.5'' vibration area if I try to let it vibrate by touching the top edge with fingers.
- Like many new notebooks, it has Home, End, PageUp, PageDown, Delete in the row with the function keys, which means I have to move my hand to use these keys. I am trying to use the number block for that, but fail yet.
- I am worried that dirt will get stuck in the speakers grid with time.
- The power cord has a 90 degree plug. If you let the cable lay to the left, it will likely be in front of the air stream coming out of the notebook (cable is thin, I don't know if it's able to make a difference).
- Had one bluescreen, likely due to a PVR attached via ethernet sending an illegal packet.
- Keyboard keys will get a bit glossy after using them.
- Managed to get vibration sounds on first run, standing on tablecloth with small profile while notebook was under cpu stress. Hasn't happened again

Bad:
- Some people complain about the air vent starting too fast, Schenker says that I happens to a few people and that they will provide an update.
- Even if only using the Intel Graphics, the processor vent is working medium to strong - I had hoped it would be less noisy if using the internal Graphics.
- On the right edge of the screen, there is a ~1'' area all along the edge with higher background illumination, letting my sharp eyes see the pixel rows if it shows a lightish grey area on the screen. That's also mentioned in the detailed test, so it likely is or was common (has also data about noise of the notebook)
- It's not recommended to use both 2.5'' slots for HDDs because the one below the keyboard can get warmer.

Schenker often has some discount, e.g. like now during the Olympics or on selected notebooks, which can be between 25 and 80 GBP. Sometimes this is coupled to a restricted component choice.
If you have questions, you can also visit Schenker's live chat on IRC: #mysn.de on quakenet.org (I expect people to have no issues with English).

Edit: The W503 has more metal parts (as far as I know, it's Clevo P150SM). The A503 is mostly solid plastic and the W355STQ (if you want to search for more info).