I've been playing about some more - it looks like the SQL string is
too long - if I do it in chunks it works. Also, some of my syntax
wasn't quite right - I've changed it to allow for no single quotes
around numeric and boolean fields.

Now I have a date field (and a time field coming up) and I have no
idea what syntax to use there (am looking around but have no help
installed on work pc). I have tried # and both with and without single
quotes.