You won't likely find a good recent model of ultrabook for under £600 but there are a few older models that fit the bill. Laptops are another story with many decent models falling under your budget limits. Here's a few really good laptops that's within your budget and should be readily available where you are.:
17.3 inch Toshiba (It's big but still mobile although it weighs more but it packs a punch)
http://www.amazon.co.uk/dp/B00GGHDH1K/?tag=ftb14-21
The ASUS Asus X550CA-XX877H if you can find a retailer with one in the UK.
This is very similar to my HP Envy I use daily and I've been very happy with it.:
http://store.hp.com/UKStore/Merch/Product.aspx?id=G7V76EA&opt=ABU&sel=PCNB
IDK, everything I can find with respectable specs or models I know from personal experience to be good solid units, don't seem to be available in the UK but those models above are pretty decent.