Unfortunately changing your URL will affect your rankings, but following best practices can help to reduce any drops which could occur. Luckily Google will actually quickly index new files with little interruption when the correct procedures are followed.

Google has published guidelines on how to change your URLs. Check out Moving Your Site from Google Webmaster Tools Help Articles. The main tips the article covers is changing your domain should be done with a 301 redirect. This tells search engines and site visitors your site has permanently moved. Google also recommends retaining control of your old domain for at least 180 days.

When you are moving an entire site to a new domain don't do a single redirect of all traffic from your old site to your new home page, but a page-to-page redirect will help protect your site's rankings in Google while providing a better experience for your users too. If there isn’t an exact match between pages on the old URL and the new one (which is highly recommended), make sure every page at least redirects to a new page with similar content.

Where possible change any links pointing to your site to the new domain, although this is probably impractical for a large proportion of your links. Just make sure all pages with incoming links are redirected to your new site. It is also important to check internal links within the old site, and update them to point to the new corresponding page. Once have recreated the content on your new server, use a link checker like Xenu to make sure you don't have broken links on your site. This tool will be particularly useful if your old site used absolute links (like www.example.com/TV/drama/Sopranos.html) instead of relative links (like ../drama/Sopranos.html).

During the switch over use Webmaster tools to submit the new site and its Sitemap and verify there are no errors. It can take a while for Google to crawl both the old and new URL, so be patient.

When you create your new domain keep the file naming and structure of the website the same if you can. For best results use the same file names which have been indexed by the search engines. For example, if you had an about page located at http://www.olddomain.com/about, it is best if your new about page is located at http://www.newdomain.com/about.

Check to see which pages are indexed on the major search engines

If you have thousands of pages on your site and you don't have the time to redirect them all, you should at least redirect all the pages which have been indexed. To find out which pages from your site have been indexed by Google use this search in Google

site:bdrlondon.com (There is no space after the :)

There are plenty of redirection tools you can use to check whether the redirects have been set up correctly. I use this one.

So if you do have to move domains it is possible as long as you follow the correct procedure.