It depends on the speed. IIRC correctly West Mids Fire have a very specific response policy, which reduces the number of vehicles allowed to travel on blues (it depends on the type of call, what the vehice is, etc) & restricts the claiming of speed exmptions to no more than 10mph.
If the driver drove in through a camera at a speed vastly above the limit and when the brigade go the NIP they found that the driver was either (a) exceeding the limit more than 10mph or (b) was not on a call/vehicle combination allowed to use lights, then they will let the prosecution go through.
It's better to arrive a minute or two later than not at all - without the full & complete details of the case it is wrong to assume the driver is in the right (& vice versa)