ValueError: unknown url type in urllib2, though the url is fine if opened in a browser

Basically, I am trying to download a URL using urllib2 in python.

the code is the following:

import urllib2
req = urllib2.Request('www.tattoo-cover.co.uk')
req.add_header('User-agent','Mozilla/5.0')
result = urllib2.urlopen(req)

it outputs ValueError and the program crushes for the URL in the example. When I access the url in a browser, it works fine.

Any ideas how to handle the problem?

UPDATE:

thanks for Ben James and sth the problem is detected => add 'http://'

Now the question is refined: Is it possible to handle such cases automatically with some builtin function or I have to do error handling with subsequent string concatenation?