Interview not reimbursed if offer is made but not accepted (UK)
This is common in the UK. In general interview expenses are relatively low. Many people take a train in the morning to the university and return home that night, so there might not be any food or lodging costs and only a relatively inexpensive train ticket. For an international candidate arranging flights and trains may require a 3 day stay, as it did for me.

I simply told the department that I was very interested in the position, but was not in a financial position to be able to cover my own interview costs if I found the departmental culture to not be supportive. They gave me a guarantee to cover the costs in writing. If your expenses are more than a train ticket, there is no reason not to ask.

Be aware, the offer may be made the day of the interview and they may want a decision the next day. The UK system doesn't really let you get competing offers.