I had a succession of Lenovo laptops from work and they were all unreliable and very flimsy, didn't last very long at all. I don't know if the more expensive Lenovos are better built?
To be fair, I think the modern trend for ultra thin laptops has led to a lot of compromises across the board with regard to components - everything soldered in instead of screwed and parts not designed to be replaceable if needed/required, along with appalling keyboards.
I'd recommend having a look at PC Specialist, where you can choose from a range of basic models and then customise the spec of various components however you prefer. Otherwise, gaming ones are usually very high spec, but if you don't actually game, a lot of your money will be wasted on a way OTT graphics card that you'll never even appreciate, much less use.
Unfortunately, I agree with PP that, although a lot of money in itself, £600 is very mid-range for a laptop. If you think about how much of the price is VAT, then the chassis, then the screen, then the basic essentials, you find that there's not a lot left for quality components where it matters.
I wince when I see laptops being offered for less than £200, because it's just a waste of everybody's money and preying on people who probably don't know what they're buying. It's the laptop equivalent of a brand new car for £5K - yes, it's a lot of money, but in car terms, it just isn't anywhere like enough for anything good. You'd be amazed that you can get a decent new laptop for that kind of money... and then you find that you can't. If that is your budget, you're better off getting doing your homework and getting a decent reconditioned one from a reputable supplier.