What spec makes a 'good' laptop?
Depends what good is. It means different things to all people. Some will class a good laptop as being light, portable, with good battery life, while others would class a laptop with high end dedicated graphics and a fast dual core processor as being good. This is evident by looking at the different opinions given in this thread about what a good laptop is.
There are different opinions because people use their laptops for different purposes, and so have different requirements.
For example, I recently bought an HP 2510p ultraportable to use at University. It has a 12.1" display, Intel Core 2 Duo ULV 1.2 Ghz processor, 80GB 4200RPM PATA hard drive and 1GB of RAM. In comparison, the speed of the processor and the slow hard drive certainly do not beat the specs of even far less expensive notebooks you can buy today, but to me, it is what I consider to be a good laptop. Because of the ULV processor, it has superb battery life, and the notebook itself is very lightweight at only 1.6 kg (3.5 lbs). It is ideal for me to carry around campus and to use on the go without having to charge up all the time.
My point is that the definition of good depends on what you'll be using the laptop for, and that different purposes have different requirements. Also, remember that it's all relative - if you're looking for portability and long battery life, then don't expect a laptop with a large screen with high end graphics.
Since you live in the UK, http://www.laptopsdirect.co.uk/
is a superb place to purchase a laptop. They have a wide range of laptops at very good prices. Use the price finder if you have a budget.