I'd fully support the refusal of entry of anyone pregnant unless it was obvious that they didn't intend to bail
There's a case for that. Under international protocols, Childbirth is considered a medical emergency, treated without question. Some people especially fly in to UK (and Ireland until they changed their citizenship laws) in order to give birth there, whether in a hospital or not.
The case is strong for getting the transfer (or proise to pay) from the person's government or insurer. But if none is forthcoming, there isn't much that can be done.
But Poles can give birth in UK hospitals without problems, and apparently many choose to. They don't usually leave the baby behind though.