Under current UK law (ANO Art 259,260), the default is that if any money ("valuable consideration") is paid ("given or promised") for a flight ("or the purpose of the flight") then it becomes at least aerial work, requiring a CPL. If money is paid for the carriage of passengers, then it is public transport or commercial air transport (covered by EU-OPS).
There is an exception entitled "recovery of direct costs" (Art 268) which allows the direct costs of the flight to be paid by the pilot's employer, or by a company of which the pilot is a director and for the flight to remain private. A condition is that neither the pilot nor any of the passengers may be legally obliged to be carried. A conservative interpretation of that is that you should always offer any colleagues you intend to carry an alternative means of transport.
'Direct costs' means the costs actually and necessarily incurred in connection with a flight without a view to profit but excluding any remuneration payable to the pilot for services as such;
That is generally interpreted to include the cost of rental, fuel and landing fees etc., but with no contribution towards maintenance or insurance.
On the human-factors side, I would strongly advise you not to put yourself in a position in which you must make a flight to get to a meeting. Leave sufficient time that you can take alternative transport. You may find that constraint quite limiting or inefficient.