Localisation Bulletin One - Spelling

An architect of my acquaintance, after listening to a certain politician espousing the Government’s latest scheme for hiving off public assets and responsibilities via ‘localisation’, declared there was no such word. They were making it up, just like the policy.
As a writer, I felt obliged to investigate. Immediately on typing the word onto my elderly grey slab of a Toshiba, I found my first clue. The spellchecker didn’t query it, so localisation clearly predates the coalition by some years.
So I went further into history and consulted a dictionary – remember them? Large books with all the words you ever knew and even more that you didn’t! My 9th edition Concise Oxford English Dictionary (which I shall now call COED for brevity) spells localise with an S, but localization with a Z. Had creeping AmericaniZation got into the COED?
Next I did a bit of weight-training – well I put the bins out – then I went for the so-called Compact Edition of the Oxford English Dictionary. This I shall call the TOB – short for Ton of Bricks. Compact it may be, lightweight it isn’t. My copy came out in 1979 and the print is miniscule. With my trusty microscope I found the letter L. The words derived from ‘local’ came between ‘lob-worm’ and ‘loch’. I dare say you could locate lob-worms in the locality of lochs, but are they localised to that locale?

Lo and behold, in the TOB, ‘localise’ does not appear. On the other hand, the verb to ‘localize’ goes back to the eighteenth century. In 1792 Mary Wollstonecraft in “The Rights of Women” talks of women being ‘localized,’ though she apologises for the word. In 1796 Robbie Burns mentions songs can be ‘localised.’
Looking at more formal sources, ‘localization’ first appears in Hansard in 1872, in a debate on local recruitment of troops. Around the same time it was also used in a number of medical and scientific treatises, but in my edition of the TOB the word is never spelt with an S.
So, localization exists and is not another imported atrocity inflicted on the English language. The question remains, what about localisation? Wikipedia allows it as the preferred spelling in the British Isles and the Commonwealth, so how come the Oxford English Dictionary has never heard of it? Today it’s widely used in medicine and scientific work, with as S. There’s even an Institute of Localisation Professionals (CLP) – no Z, does this mean they are on the coalition’s side?

P.S. As my architect friend has just pointed out to me, the word he was querying was not ‘localisation’, which I have enjoyed pontificating around, but ‘localism’. Unlike our political masters I am quite willing to own up to not listening to people. Therefore subsequent bulletins will be re-named Localism Bulletin.