I have found that to a certain extent it depends how old you are and where in UK you were educated. I am in my 50s and educated in Scotland and I was taught to use -ise. I understand that the -ize ending is becoming more common now as it is used in the OED and also is the American spelling. You pays your money and takes ypur chance in crosswords
Thanks Scotman I am mid sixties and educated in Scotland also, as you say you take a chance with croswords, but to have three of them in the same crossword!!! I will stick with the ise this time and look carefully next week at the solution.
The American spelling certainly uses 'Z', but I'm fairly sure that the spelling with 'S' is relatively recent in the UK. My Shorter Oxford E.D. of 1973 gives the 'Z' version only, while my up- to-date dictionary gives the 'S' version as the preferred one, with the 'Z' second.