Thanks to @[deleted] and @[deleted]
Both these actually worked but the problem was - not in a word document as part of the mail-merge. It kept throwing an error "Invalid Tag Expression" The mail-merge I was trying to do had the code <<REPLACE_PATTERN( BO.address, CR(),', ')>> (actually trying to fit an address containing 5 single elements into a space designed for someone to write into (a membership application form)
I ended up getting round it by creating a non persistent bo just before the call to do the merge NPBO.addresstext=REPLACE_PATTERN( BO.address, CR(),', '), then putting a simple <<BO.addresstext>> into the word doc.
Thanks again guys