htaccess no funciona como se requiere

Firstly, you have some stray spaces in your mod_alias Redirect directivas:

Redirect bootstrap/engagement-ring.php http://www.mydomain.co.uk/bootstrap/engagement-    ring

Redirect bootstrap/inferno-diamonds.php http://www.mydomain.co.uk/bootstrap/inferno-    diamonds

These will cause a 500 server error, because it has the incorrect 3 parameters.

En segundo lugar, tu Redirect directives need to match against a leading /, so they all need to look like:

Redirect /bootstrap/rolex-watch.php http://www.mydomain.co.uk/bootstrap/rolex-watch

But those 2 issues are really just moot because you've created a redirect loop by rewriting the URI with your last rule, and redirecting de nuevo mediante el Redirect statements. The two different modules that you are using, mod_alias (Redirect) and mod_rewrite (Rewrite*) both get applied to the same URI at different point in the URI processing pipeline, and thus they both mangle the same URI. You need to stick with just mod_rewrite and add a check at the very beginning to prevent looping altogether:

# This prevents the rules from looping
RewriteCond %{ENV:REDIRECT_STATUS} 200
RewriteRule ^ - [L]

RewriteRule ^bootstrap/products/(.*)/(.*)/(.*)$ bootstrap/products.php?f=$4&b=$5&t=$6
RewriteRule ^bootstrap/products/(.*)/(.*)$ bootstrap/products.php?f=$4&b=$5
RewriteRule ^bootstrap/products/(.*)$ bootstrap/products.php?f=$4
RewriteRule ^bootstrap/products/search/(.*)$ bootstrap/products.php?s=$1

RewriteRule ^bootstrap/rolex-watch.php http://www.mydomain.co.uk/bootstrap/rolex-watch [L]
RewriteRule ^bootstrap/scrap-gold.php http://www.mydomain.co.uk/bootstrap/scrap-gold [L]
RewriteRule ^bootstrap/eternity-ring.php http://www.mydomain.co.uk/bootstrap/eternity-ring [L]
RewriteRule ^bootstrap/engagement-ring.php http://www.mydomain.co.uk/bootstrap/engagement-ring [L]
RewriteRule ^bootstrap/wedding-ring.php http://www.mydomain.co.uk/bootstrap/wedding-ring [L]
RewriteRule ^bootstrap/diamond-ring.php http://www.mydomain.co.uk/bootstrap/diamond-ring [L]
RewriteRule ^bootstrap/inferno-diamonds.php http://www.mydomain.co.uk/bootstrap/inferno-diamonds [L]
RewriteRule ^bootstrap/radley-products.php http://www.mydomain.co.uk/bootstrap/radley-products [L]

RewriteRule ^([^\.]+)$ $1.php [NC,L]

Thanks Jon Lin, but it didn't quite work for me.

I seem to have bluffed my way to something that does work. Some entries I didn't need.

Is it written efficiently as I have no options defined?

RewriteEngine on
RewriteBase /bootstrap/

ErrorDocument 404 /bootstrap/404.php   
ErrorDocument 403 /bootstrap/403.php 

RewriteRule ^products/search/(.*)$ products.php?s=$1
RewriteRule ^products/(.*)/(.*)/(.*)$ products.php?f=$1&b=$2&t=$3
RewriteRule ^products/(.*)/(.*)$ products.php?f=$1&b=$2
RewriteRule ^products/(.*)$ products.php?f=$1

RewriteRule ^([^\.]+)$ $1.php [NC,L]