unless there are spcific signs limiting loading time
(or kerb clips limiting when the loading exemption does not apply)
then as much time as necessary and reasonable is allowed
loading needs to be continuous but includes time for
paperwork and arranging items at their destination
but not having a cuppa
see patas jane packer v westminster
http://www.parkingandtrafficappeals.gov.uk...nts/LOADADJ.pdfcontains pretty mcuh all you need on the loading exemption
note with a big van you could still maybe be done for obstruction