Heavy Brute Force attack?

Hi

Im tryig to login to my word press control panel to update my site (http://www.nsk.org.uk/wp-login.php) and im getting this message: –

“This page is temporarily not available and will be available soon.
Currently the wp-login.php script is under a heavy brute force attack. We have temporarily blocked access while the attack is present. Once the attack subsides access to this script will be restored.

We apologize for any inconvenience this may cause and appreciate your patience.”

Any idea why and what I can do?