Thanks for the replies, guys!
Okay... I've been using the Google tool a bit, and so far it seems okay, although the interface is a bit tricky for extended sessions and it seems very much guess work based. On the bright side it does show up the keywords which we know are being search for, which Wordtracker spectacuarly failed to do.
As for Keyword Discovery... I actually used that for a good while, and found the results a bit suspect there as well. Really oddly ordered phrases outranking sensibly written ones and such - true, I can't prove it was wrong, but it felt a bit fishy nonetheless. Secondly, the data for UK searches was recorded over a really long period IIRC, although they didn't specify what it was. Given most our work is travel websites, this is tricy because searches are seasonally dependent.
Also, they say they get their data from Yahoo, Google etc - I thought none of the major search engines revealed their numbers... isn't that right?
Thanks for your continued help in unraveling this mystery
Sticklebrick