Since you mentioned the memory bit I'm guessing Hard Drive space. How much would you need? 500, 640 or 750GB? For those activities listed I think you'd need at most 4GB of RAM. In case you need more you could always purchase more RAM at the hardware shop and have them insert it for you or do it yourself. Since you're not going to be using it for gaming, you can probably get by with an integrated graphics card rather than a dedicated one.
The brand I recommend is Asus or Toshiba due to their superior build quality. You'd want to avoid Acer unless you're looking for a throwaway laptop. Their builds are horrid and I've had lots of issues with them. HP is along the middle, neither good nor bad.
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15.6 inch Laptop
Intel Core i5-2450M 2.5/3.1GHz
Windows 7 Home Premium
-There's another version where if you add £99 you'll get 2GB more RAM and 160GB more HD space. The processor is pretty solid, even better than the one I'm using atm. It's a 2nd gen i5 processor which is as good as the 1st gen i7 processor (which was used for heavy gaming).
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15.6 inch Laptop
Intel Core i5 2450M 2.5GHz,3.1GHz
Windows 7 Home Premium 64-Bit
It's a bit pricier but has the same processor and RAM as the previous laptop listed. It also has 50% more HD space.
Not sure if they're to your liking but there's a bunch of other 400-500 range laptops listed on Amazon UK: You are not allowed to view links.
My current laptop is an Asus A53S with the following specs:
15.6 Laptop Screen
i5-2410M 2.3GHz, 3.1GHz (with turbo boost)
8GB RAM (free upgrade from 4GB originally)
Nvidia GT540M Dedicated Graphics Card (2GB VRAM)
Win7 Home Premium
But it's an outdated piece of hardware by about 6 months. I use it mostly for school and gaming (it can run all the latest games without a hitch). I've still got about 300GB free despite all the games and downloads.
My advice is to stick with Asus or Toshiba. HP and Dell are still OK but you should never go with Acer if you want value for your money. It's the crappiest brand out there.
Anything with a 2*** after the i3/i5/i7 is a 2nd generation processor. The ones with 3** are 1st generation and about a year outdated. Currently the latest laptops are using 3rd generation. You can tell which ones they are by the 3**** (4 digits compared to 3 digits 1st gen). eg: i5-3427U.
Hopefully that helped >_<