Hello StevieWeavie
I haven't opened up the MacBook yet because I want to start from an ISP that's already in place
Even if you don't download games or DVD's you still should get a broadband connection. That being said your mac book does not come with any preconfigurations for UK ISP's.
If your a light user you can get ADSL and Cable broadband for as little as £9.99 per month. However in some cases your montly bandwidth limit is capped.
Beware that many ISP's will tell you they don't support Macs. This is because the usb adsl modem they supply is not supported on the Mac. However all UK ADSL will work on your mac if you purchase and use your own Ethernet ADSL router.
Get a package that would allow you to upgrade in fthe future don't get tied into a 12 month contract, many isp's allow 1 month or 3 month contracts. You say you dont do fancy downloading however once you have broadband you may getinto using Voice over ip to make free phone calls. You may do video chat. You may get into TV on demand, Software updates are getting bigger and bigger.
As your in london you may be able to get telewest broadband
they are cheap and reliable and provide a free ethernet cable modem.
http://www.telewest.co.uk/websales/service.do?id=2
If you want mega fast broadband check out
http://bethere.co.uk they also provice a free ethernet wifi adsl router.
Also check out the
http://adslguide.org they have lots of info on UK isp's