We bought this from John Lewis last week at £449, it's now dropped down to £399 which seems to be the lowest I've seen it at - I've already had the difference refunded :)
It's not 10 bit, and it's not OLED, and it's not over £1000 either.
It is a good quality, 8 bit UHD TV for under £400.
Some people will say 4k is pointless on a 40", but after watching Star Trek in UHD at the weekend I can honestly say there is a big difference in quality from HD.
Credit to cd81's deal posted yesterday (Same price at Richer Sounds), but for me John Lewis is a better option with Free delivery rather than store collection only Richer Sounds.