permalink redirect via htaccess

Thanks for your reply. However old url is not redirecting to the original post, but redirecting to the homepage. Here’s an example:

Old URL: http://primenews.uk/en/2015/02/07/delhi-votes-test-modi/
New URL after changing permalink: http://primenews.uk/en/?p=2351

my .htaccess in /pubic/en/

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^old-slug$ http://primenews.uk/en/new-slug [L,R=301]
RewriteBase /en/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /en/index.php [L]
</IfModule>

# END WordPress