With Hailo you will always get 2.5 minutes free waiting time, and the driver will not charge you anything until you get in the taxi, or until the free 2.5 minutes waiting time has passed.
In a London taxi, when the meter is started, it will show a price of £2.40. This is a standard charge for all black cabs across London. If your driver has been waiting for longer than 2.5 minutes, or you requested to be picked up from a different location to the one you booked, you may see more on the meter.
However, if you still think the meter was showing an excessive charge when you boarded, ask the driver why the meter was started. Alternatively, please give us all the details including the job reference number located at the bottom of your email receipt.