Thomson 585v7 Reset - Administrator logon

[#1]

I have a problem with the Administrator password, which is completely stopping me from logging on to my router.
Whilst I had a line fault I ended up restoring my Thomson 585v7 router to factory defaults.
Initially I could access the router (192.168.1.254) with no password prompt, and I set my account name etc. Then I tried to add a new admin user (prior to changing the admin password) and at this point it prompted me for username/password. I could not get past this prompt. Now I cannot access any router page at all as I always see the username/password prompt when accessing 192.168.1.254.
I've tried several usernames, but mostly "Administrator". I've tried many passwords including the serial number (with case variations), blank, and the password I'd previously used. No luck.
I've tried a hardware reset, but this appears to be disabled. I can't do another software reset or a restore because I can't log on to the router.
Does anyone have any idea what the Administrator password could be after a reset?

[#2]

Hi,
By default the username should be either Administrator (with a capital A) or admin (all lower case) and the password should be the serial number of the router (in capitals but not the bit in brackets after it).
If that doesn't work let me know and I can send you out a Netgear instead.

[#3]

Hi Dave,
The password is definitely not the serial number; if you could replace it with a Netgear that would be great.
Many thanks
Richard

[#4]

Hi Richard,
Ordered it Wednesday evening so should be with you today or tomorrow. There's a link to the setup guide in your ticket.