read what you sign as it states that you
1 wear seat belts at all times driving or passenger (no exemptions)
2 do not use any electronic devices whilst driving/moving IE: PDA or mobile phones
3 Do not smoke in Royal Mail vans
failure to follow these conditions is Gross misconduct
I believe your local manager will have there bottom kicked if a safety audit is carried out
As I've said before .... do your job the way Royal Mail expects and if your late back, Book it or return following correct cut off procedure
cutting corners only cuts your own throats ....
Tell your manager the first pillar is safety first