For a 40" 4K TV this is a cracking deal from AO.com.
With this voucher code 4k10
You can get the TV deal for £269.10 delivered. It also has built-in Wifi so it's a Smart TV, with 2 years warranty.
If you have Android it has an app you can use to control it and install other apps which is cool. For example, you can stream videos from your phone to the TV.
Also, if you do get this deal, make sure you have a look at the sound bars on offer - you get a special price for these too.