Hi Pat,
In our case, I was not able to get a provisional booking.
I was told by 2 superintendents in my region that a booking was not possible until my fiancee has been in the UK for 8 days. The ECO will be aware of this... their guidance notes state
"The Entry Clearance Office (ECO) needs to be satisfied that it is intended that a marriage in the UK will take place. Any evidence that may be available that wedding arrangements are in hand may help in this respect. Failing that, the ECO can reasonably expect you to have made some tentative plans for the wedding. The ECO will, however, be aware from our published procedures that "the law relating to marriage in England and Wales does not allow for any arrangements to be made with a Registrar until the foreign national has arrived in the UK"
In our case, I have made a provisional booking for a wedding reception, with a given date. I also stated in the cover note that I had spoken to superintendents who advised me that provisional bookings are not possible. Given the above, I am now of the opinion that ECO's could look sceptically upon any such documentation anyhow (after all, the laws of the land state this is not possible). I am not dismissing what others have done, because it still serves the purpose that wedding arrangements are in hand. Trying to get this document delayed us somewhat, and in the end we had to go without it. I just hope that the wedding reception booking will suffice.
Good luck with the application.