Using mod_rewrite() on 1and1 shared hosting - php

Question

Update
I couldn't get this to work adding rules to the .htaccess file, in the end I used the Wordpress Rewrite class and added an add_rewrite_rule() to do the re-write which worked perfectly.
Original Post
I have been trying to put together a .htaccess rule to move parts of the path to a query string. As per https://wiki.apache.org/httpd/RewritePathInfo.
I have two folders in the root of my webspace, one for www.mydomain.com and one for test.mydomain.com. My .htaccess file is in the test.mydomain.com folder, and I want to rewrite test.mydomain.com/images/parm1/parm2 to test.mydomain.com/images/?gwpw=parm2&gwpi=parm1.
If I put garbage in the .htaccess file I get a 500 internal server error so I know the file is being read. I also have some existing rules in .htaccess from Wordpress that use mod_rewrite(), which if I comment out, stop the site redirecting to a 404 error page if you try to access test.mydomain.com/somegarbage. So I know mod_rewrite() is enabled.
I have read I need to set Options +FollowSymLinks -MultiViews, so the whole rule I have is:
Options +FollowSymLinks -MultiViews
RewriteEngine On
RewriteBase /
RewriteRule ^/images/([^/]*)/([^/]*) /images/?gwpw=$1&gwpi=$2 [PT]
I have tried this in different parts of the file, removing the leading slash from /images/?gwpw=.... I've tried adding a rule that I thought should rewrite every request to a different page like RewriteRule ^/* /somewhere but I can't seem to get any rewrite to work.
As this is a shared server I can't access httpd.conf.
My entire .htaccess file currently looks like this:
<IfModule php5_module>
php_flag session.cookie_httponly on
</IfModule>
Options +FollowSymLinks -MultiViews
RewriteEngine On
RewriteBase /
RewriteRule ^/images/([^/]*)/([^/]*) /images/?gwpw=$1&gwpi=$2 [PT]
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
# Wordfence WAF
<Files ".user.ini">
<IfModule mod_authz_core.c>
Require all denied
</IfModule>
<IfModule !mod_authz_core.c>
Order deny,allow
Deny from all
</IfModule>
</Files>
I am a complete newbie when it comes to .htaccess rules, so any help would be greatly appreciated. I'm clearly doing something wrong but I can't see the wood for the trees anymore!