When Doyle is talking on the radio to Cowley about Dunston, he is driving along a road alongside fields. When he is next seen a second later, after a brief cutaway to Cowley, he is driving down an urban residential street.
Banknotes weigh 1gram apiece. 1million pounds in denominations no larger than tens would therefore weigh 100kg minimum. A strong person could lift this but no way sling it around like they do in its case.