Re: Lawyers' opinions are just that...
Here's what section 2 subsection (7) says:-
"For the purposes of this section the times while a communication is being transmitted by means of a telecommunication system shall be taken to include any time when the system by means of which the communication is being, or has been, transmitted is used for storing it in a manner that enables the intended recipient to collect it or otherwise to have access to it."
Source: http://www.legislation.gov.uk/ukpga/2000/23/section/2
Note in particular the words, "is being, or has been, transmitted", and, "to collect it or otherwise to have access to it."
"or has been" is explicit, and clearly distinct to "is being". "or otherwise to have access to it" is explicit, and clearly distinct to "to collect it".
If 2(7) only meant that "A message is still considered in transit even when stored on an e-mail server, where the intended recipient hasn't yet collected it", but didn't include times after which the message has been collected, it wouldn't say, "to collect it or otherwise to have access to it." It would simply say, "to collect it". "or otherwise to have access to it" clearly means storage other than while awaiting collection. "or has been" explicitly includes those times after which the message has reached its final destination within the "telecommunication system", and therefore includes those times after which the message has been collected but is still being stored within the system.
IANAL.