under a seven decade-old UK US agreement on intelligence sharing
Britain and America spy agencies are not supposed to collect information on each
other
without permission according to the Guardian newspaper on Channel 4 News
in 2007 existing rules were modified to allow the US to retain more information
about British communications
which the collected incidently as part of its global information gathering
operations
previously anything other than landline phone numbers could not be kept
but after 2007 mobile phone numbers and email addresses could be retained
this information it appears with them be used as part of what's known as contact
chaining
analyzing which numbers or email addresses were in contact with others
which might be of interest this appears to have been done with British consent
listening to a phone call or reading an email though still required a warrant
from the British government
it is also claimed the 2005 memo raised the possibility of the US carrying out
surveillance
on British nationals without which is permission when it was considered to be
in the
US national interest but it's not clear if that proposal was acted on