Webmaster Tools is showing duplicate content for:

mysite.co.uk/
&
mysite.co.uk/index.php

Is it worth doing a 301 redirect for / to go to /index.php?

Also, GWT is showing index.htm (which doesn't and has never existed) as being blocked by robots.txt (which it isn't) - again, I've done a 301 redirect from index.htm to index.php - have I done the right thing, will it solve the problem?

Thanks in anticipation

You should redirect the index.php page as most people will link to you using just your domain not the index.php

Thanks

So, just to clarify: I can 301 /index.php /index.htm & /index.html to / without causing an infinite loop?

Do you have versions under index.htm and index.html? I think redirect - syntax-wise are different for each type. As long as you use the right one, you should be fine.