The lowest point on the outside would be around the top of the
skirting board on the inside, so I'm guessing I'd still have a
proble.

The whole point is that the injection is done above the outside ground
level. Otherwise, you are swapping no DPC for a bridged one, which may be
better, but possibly not by much. The problem is that your floor level is
low, making it partly cellar.

Christian.