//The cost of administering a nominal £50 charge such as you mentioned would make it almost useless.
Generally speaking my answer is, no to charging.//
Back in 1979 I had an ambulance ride after being knocked from my motorcycle by a careless driver. A few weeks later I received a bill from the L.A.S.. It was about £80 I think.
I think an ambulance callout (Paramedics and Full Kit) is about £300 per shout.
I sent the bill to my insurance company. The cost was payed by the defendant at court when answering a charge of Driving without due care.