If you do a business trip and carry other company employees, that's OK too, on a PPL. Just make sure nobody is obliged to FLY (i.e. can take a train, etc). The grey area is when you carry customers, etc......
To expand on this, I have seen material from the CAA that essentially says that it's OK for a PPL to take colleagues, customers and whatnot on a private flight, IF the flight is only incidental to the trip.
In other words, there has to be a viable alternative. Car, train, commercial air transport, whatnot. So if you fly to and from a business meeting it's OK. You could have driven there as well. But once you start using the aircraft for, for instance, survey work, you're in trouble. Since the survey work could not have been done by car.
The other stipulation is that your employer can't force your colleagues to fly with you. They have to provide an alternative if they don't want to fly with you.
And under these conditions it's perfectly OK to get reimbursed by the company for all the direct costs. But as Peter said, it's a bit of a grey area what to consider direct costs, if you own the plane.
Having said all that, you do need to be careful in considering this. As you know well by now, VFR flying in a light aircraft is very, very dependent on the weather. But your colleagues and the customers you are visiting might not be so understanding, as their experience is probably with commercial airlines only. So if you cancel a trip at the last moment because the weather looks iffy, they're not going to be happy. Do that too often and your performance and standing in the company suffers. (And that's not even considering the opinion of your colleagues when you show up with a clapped-out C172, instead of your shiny new company car.)