I now do have the complete message, and I believe that the cells containing numbers should possibly be discarded, but am uncertain as to how to arrange the remaining letters. (If this is indeed correct). Have tried several ways but achieved nothing yet.
Good luck, Keith - let me know if you get to the answer! I couldn't work out what I was supposed to be doing, how to read the message, whatever. People on Answerbank have done it - I must be particularly dense.