Taxi
Depending on where you are heading, taxi may be a good choice.
There is a taxi rank just by platform 10. It’s well hidden. On the times we have tried to use it, it was empty.
There are also taxis outside the station near where McDonald’s is located.
The railway station is very busy as it is also a big commuter station, and our experiences have been poor. If you are lucky you will just have a long queue.
You can also try the main roads. Exit the ticket barrier from your train and turn left and up the stairs or escalator at the end, near W H Smith, onto Bishopsgate. To head towards London, cross the road at the crossing and you might see a free taxi go by.