Some good finds!
Assuming it's just for everyday use, out of the four I think I'd go with:
http://www.saveonlaptops.co.uk/Lenovo_Ideapad_U310_UltraBook_1256867.htmlWith this you have the older processor (2nd gen, 4th gen just been released) however you won't notice a massive difference with everyday use.
It also has the SSD/HDD combination, this means the laptop will start up in around 10 seconds and be ready for use, a massive plus point I think
Although it has no optical drive, you can buy ones that connect via usb if you wanted to play dvds, so I wouldn't make a decision based on that.
I'm guessing you're happy with 13", so that will help make it more portable. Also Lenovo are known as a good brand for laptops!
Also has the claim of 6-7 hours battery life!
http://www.saveonlaptops.co.uk/ASUS_VivoBook_S400CA-CA071H_1336282.htmlThis is very similar to the Lenovo, It doesn't have the SSD so it'll be normal boot up speed . It has the same processor and also hasn't got an optical drive, the only advantage this has over the Lenovo is the screen being bigger, personally I'd stop thinking about this one out of the four.
http://www.saveonlaptops.co.uk/Samsung_370R5E_1318487.htmWith this, you have the 15" screen, so a little less portable, but not massively less. The processor is newer and has almost twice the power, but again with everyday use the differences won't be huge. Again no optical drive, and also no SSD, but to be fair the only place the SSD is going to make a difference on the lenovo is the speed of the OS (boot up etc...)
http://www.saveonlaptops.co.uk/Toshiba_Satellite_P845T-10G_1349498.htmlThis has an optical drive, something the others doesn't. It has the newer processor but as I said, this isn't massively important. If the claims on battery life are true, 5-6 hours is decent!
Overall (all of this is just my opinion), they all have pretty much the same storage, the Toshiba and Lenovo offer the best battery life with the Lenovo being the most portable. The samsung is the most powerful but the Toshiba is the only one to have an optical drive but as mentioned these can be brought, so out the 4, I'd pick the Lenovo!