Hello,
index.html is the default page name on your server, so for browsers the two links
http://www.server.co.uk/ and
http://www.server.co.uk/index.html are equivalent. About search engines robots we are not so sure, we believe that Google robot is intelligent enough to consider ‘/’ and ‘/index.html’ pages also as equivalent. However, we also think that it is better to use one form of URL through the entire site, therefore we list all variants of URLs found on your site just to give you an overview of all the links used on the site.
About the PR redistribution: the best strategy is to determine a few most important pages on the site and minimize the number of outbound links from these pages, and maximize the number of inbound links from all other pages. The important pages can link to each other; this would not affect their PR too much.
Best regards