Welcome to the forum, Przemek!
As for maximizing your battery life, there is another very good thread
★★★★★ discussing this, see
GUIDE: How to max out your battery life *56K warning - Pics* which will point you to the "Notebook Hardware Control" (NHC) program, that can be used to keep power consumption down - and therefore battery time long! You may download NHC via the thread
NHC 2 is out! and then get the "ACPI"-file as discussed e.g. -->
here - and then you're simply in
cool 
business!
Note: By using NHC to "undervolt" the CPU you don't loose
anything (except in some cases the high fan noise and any case the "short" battery time!); what you do is adjust
your particular, specific/personal CPU the minimum voltage setting which is
sufficient for stable performance - in stead of continue using the default and a bit too high CPU voltage that Intel has specified to make sure that
all CPU's would run (the thing is simply, as already said, that most CPU's will actually run exactly as well with slightly lower voltages - and that's
your job, using NHC, to find out how low you can go!). The same about the GPU clock speed; downclock it and save power.
To find more information about extending battery time on ThinkPad's, I honestly don't believe you need to go elsewhere... because
this! is surely the ThinkPad forum Number 1! Rather I suggest you get yourself a bit acquainted with the
Search-function available here - and then you can dig up a wealth of useful information yourself!
As for batteries in London... I am sorry, but I don't have a clue (except
www.ebay.co.uk). Hopefully some English forum members can help?
Best regards,
Johan