All went well, but it seems that periodically WP rewrites the htaccess file to only include the default WP lines.
I added the lines within the block of wordpress lines which may be part of the problem?
So my htaccess file looks like the solution offered on this page.
Can anyone shed some light on why WP intermittently rewrites the htaccess file, whether the problem is including new lines within the WP block and if there is an alternative working solution?
Many, many thanks.