Well, sourced it out. Ealing may just be greedy bastards! No other borough sites I've looked at mention this...
Quote from their website:
"The Notice of Marriage must state the venue where the marriage will take place. Do not arrange to give your notice if you have not decided on the venue. The notice is not transferable to another venue so, should you change your mind, this would require a new notice and an additional fee."
There ya go. So I suppose the above means that if we decide to change the venue, we have to give another notice to our borough. It may just be cheaper in the long run coz then I can just get the spouse in the states instead of getting one then the other.