Re. Splitting the tip with the driver..... it's but a short step to 'but we tip taxi drivers'. And hairdressers. And doormen.
I think in the case of of drivers and hairdressers, this really is a hang over from the olden days - but almost impossible to shake off.
Re. Doormen (at hotels etc), I've found that tipping them pays well.
Re. The OP. This was tantamount to 'monetary extraction'. In the UK, if there is a tour ride - then what *might* happen is a sweep stake of all the passengers with (for example) a guess as to the mileage covered that day. The proceeds of the sweep go half to the person who guessed nearest and half to the driver, or perhaps the 'winner' gets a souvenir from one of the places visited and the driver scoops the pot. At least this way, there's a bit of fun/entertainment and one can opt out if one wishes.