hashtag bloody cyclist

[Grahamm]

do you really think you'd get charged for helping emergency services?

Unfortunately, according to the letter of the law, yes, you would.

Having done some searching on this, sometimes fines are waived, other times they aren't. Also I've found this from TFL's website:

When can I enter a bus lane?

    During non operational times. The times of operation are indicated on the sign
    If you want to turn left within 20 metres of the junction - an arrow or a dotted white line will indicate if this is allowed
    If avoiding road works or emergency vehicles

So, at the moment, the law is, frankly, a complete mess...!