tanith recently I had to go as an emergency from home to Moorfields, City Road and it cost me £15 to go there. I appreciate that you live further out than I do but the problem is getting a mini cab from inner London to where you live costs a lot more. Why do you not ask your local mini cab company how much it would cost for one of their drivers to pick you up from OPD? That is what I did going home because the inner city firm wanted to charge around £20.
If you were certain that you would not be going for xrays or whatever, maybe your DH could ring the company when you are called to see the surgeon and that would save time hanging around.
It would be cheaper and more pleasant to have a fish and chip supper close by and catch a marginally later tube and with luck the majority of the rush hour punters will be on their merry way.