Ubuntu-minimal is installed:
wookey@e102475-lin:~$ apt-cache policy ubuntu-minimal
ubuntu-minimal:
  Installed: 1.207
  Candidate: 1.207
  Version table:
     1.207+aarch64v1 0
        500 copy:/srv/repos/ maverick-aarch64/main amd64 Packages
 *** 1.207 0
        990 http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ maverick/main amd64 Packages
        100 /var/lib/dpkg/status

So I'm not sure why update-manager can't find it.

here is my /etc/apt/sources.list

### This source file has been modified to point to ARMs internal mirror which houses most repositories. 
### We currently not keep the multiverse repositories locally based on the definition of the contents 
### outlined by Ubuntu/Canonical. The Sources are still available and are left unmodified below where needed.
### Please read the guidance on the difference between the different package types provided by canonical
### here:- http://www.ubuntu.com/project/about-ubuntu/components

### Wiki location for ARMs mirror setup:- http://wiki.emea.arm.com/Sysadmin/UbuntuMirrorUser

deb http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ maverick main restricted universe
deb-src http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ maverick main restricted universe

#deb http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ natty main restricted universe
#deb-src http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ natty main restricted universe

deb http://e102475-lin/obanrepo natty-aarch64 main

## Major bug fix updates produced after the final release of the distribution.
deb http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ maverick-updates main restricted universe
deb-src http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ maverick-updates main restricted universe

deb http://gb.archive.ubuntu.com/ubuntu/ maverick multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ maverick multiverse
deb http://gb.archive.ubuntu.com/ubuntu/ maverick-updates multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ maverick-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
#deb http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ karmic-backports main restricted universe 
# deb-src http://arm-archive-ubuntu.cambridge.arm.com/ubuntu/ karmic-backports main restricted universe 
#deb http://gb.archive.ubuntu.com/ubuntu/ karmic-backports multiverse
# deb-src http://gb.archive.ubuntu.com/ubuntu/ karmic-backports multiverse


## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu karmic partner
# deb-src http://archive.canonical.com/ubuntu karmic partner

#deb http://arm-security-ubuntu.cambridge.arm.com/ubuntu/ karmic-security main restricted
#deb-src http://arm-security-ubuntu.cambridge.arm.com/ubuntu/ karmic-security main restricted
#deb http://arm-security-ubuntu.cambridge.arm.com/ubuntu/ karmic-security universe
#deb-src http://arm-security-ubuntu.cambridge.arm.com/ubuntu/ karmic-security universe
#deb http://security.ubuntu.com/ubuntu/ karmic-security multiverse
#deb-src http://security.ubuntu.com/ubuntu karmic-security multiverse