At £200 you are cutting it a little fine to get a decent laptop regardless of the spec.
A genuine 3hr battery life is common now (though amazingly there still are loads of new laptops with a ~1hr battery life) but it was rare a few years ago. Also a used laptop is likely to come with a partially knackered battery and most laptop batteries cost ~ £100 and even that usually only gets you a counterfeit one from Ebay.
I routinely buy laptops in that price range for my work (for use in test rigs which are shipped out to China where I get some stuff assembled) and while they work fine they are basically tatty and well worn and you can forget the batteries.
£300 opens things up a lot more, with plenty of good stuff, and I have just bought a really nice Thinkpad T42 for £380 (14", 1GB RAM, 30GB HD) which is totally unused and in the original box with a 12 month warranty. But with a US keyboard - beware this common little trick!
People will recommend as many laptops as there are people you ask. I like Dell and IBM/Lenovo. You need to decide whether you want a lightweight 12" one; they do cost more than the 14" ex corporate workhorses. Personally I use a Thinkpad X60s-1704 (12", 8hr battery life and built-in GPRS/3G) and very light, but you won't get an x60s for much below £600.
I also used a Dell Latitude L400 lightweight 12" one for a long time and it still works perfectly; you can pick these up for £200 and it's a super machine. But... battery will never make 1hr and no built-in wifi. This one lives in the boot of the plane when I go on long trips; it has a duplicate of the x60s config on it.
The high street consumer laptops are mostly of crap quality (basically anything below £700 new) and are best avoided. The best buys are the corporate-grade laptops sold either unused or refurbished by firms such as
this one and a google for "refurbished laptops" turns up a load more. Ebay is another source but I find the prices on Ebay are no lower than elsewhere and since most of the vendors have no telephone number one can't easily check small details like whether the keyboard is a UK one with the £ sign...