The 40PUK6400 has a maximum display resolution of 4K Ultra HD. That's over four times the display resolution of the most common HD type of Full HD. 4K Ultra HD TVs have a resolution of 3840 x 2160 pixels.
A 4K Ultra HD HD type is actually the best display resolution amongst all TVs of a comparable spec and age to the 40PUK6400.
The worst display resolution amongst similar types of TV is HD Ready.
4K Ultra HD TVs have a resolution of 3840 x 2160 pixels.
There are a number of other 4K Ultra HD TVs currently available that you might want to look at including cheaper televisions such as the 40UF7707, or the 49UF640 (£489.99) both from LG.