400 is a bit tight, I'm from the UK too, and although you can get Sonar to work on one at that price, when you push it a little, it will creak a bit. I am currently on a that level of Laptop, and am holding out for a laptop here to meet my specs demands (In fact I may have just found mine yesterday (a HP Envy DV6))
My suggestion would be
Aim for an i7 (otherwise i5)
Minimum 4gb Ram, unless you are looking at lots of sampling use (check to see if it can be expanded to 12-16gb, if it's 12, then you are keeping the original 4gb and adding an extra 8, but if it's 16gb, you can later ditch the original 4 and add a matched pair of 8's, which is advisable to match)
Most laptops have 5400 drives, and this is easily expanded on later when funds are available for a better and faster 7200rpm drive. Some are using Hybrid drives now, which is a mix of SSD and standard drives. If you want to expand to SSD, then it's good to have a 2 drives, and in a laptop this means dropping the CD drive out and adding a hard drive here. Not all laptops have cd drives now, so having one included makes this an option
Minimum 3 USB's, one for you soundcard (you do have an external soundcard already I hope), one for a Midi controller, then one spare (mouse, harddrives, etc)
Cakewalk advise 1280x800 minimum screen resolution, and laptops tend to be, 1366 x 768, which is workable, but you notice the missing height at times. HD should be 1920x1080, some laptops say they are HD, but are 1366x768.
My suggestion would be, make sure you have an external soundcard, and push the budget further on the laptop, you will most likely regret not doing so later.
Found this, I am not endorsing, I haven't checked the RA expanding options.
http://www.dabs.com/produ...efs=54600000&src=3