To gain access to your Nominet account, you will need access to the email address that you registered the domain name under.
Go to https://secure.nominet.org.uk/auth/access-your-account.html and enter the email address your domain name is registered under in the Email Address box.
Click on the Access Your Account button.
If you have entered an email address that is associated with a Nominet account, you will receive an email containing a link in which you can reset your password. Simply click on the link, define your password in the New Password and Verify New Password boxes and then click on the Update button.
You will then be taken to the screen displayed below. Click on the log in link to be taken to your Nominet account login screen.
Enter your email address and password in the relevant boxes and click on the Log in button.