Technicolor TG582N - default username and password?

[#1]

Help!! I've reflashed my Technicolor TG582N router with Plusnet firmware, and am now unable to login to configure the router. I'm locked out! Does anyone know the factory default username and password?
I have done a long reset (till power LED turns red) so it's all back to factory default settings.
The router is TG582N DANT-T variant.
Firmware image I flashed onto it was PN TG582N R844J.bin
(I used the firmware update utility from BE to do this, but that shouldn't make any difference)
So now the user & pwd are different and I can't get in. I've tried every combination of [blank]+[blank], Administrator, Admin, admin, serial number, access key etc.
If I can get into the router I want to change the firmware again to the +USB version of 844J so that I can have 3G dongle backup option for when I take the router with me on a caravan holiday -what will be the user & pwd for that version (if different again)?
Many thanks!

[#2]

Done it... I'm in.
It was admin and serial number. Which I had tried before, but s/n was wrong - I misread a 5 as an S. Stupid font on router label, making a 5 look like an S. So have a good long close-up look at the label underneath the router with a magnifrying glass if you're having trouble like me.
According to PlusNet website, depending on the age of your TG582N, there are 3 possible sets of default login details:-
Administrator
serial no.
Administrator
blank (no pwd)
admin
serial no.

[#3]

As far as I'm aware the router username and password on the TG582n has always been admin and serial number respectively. The previous alternatives mentioned applied on a much older router, the TG585v7.