I think it's definitely the lack of supporting evidence of the intended small-scale wedding.

As I've mentioned previously, we have submitted the letter from the local Register Office, confirming a provisional wedding booking showing the date and time.

It seems that the ECO feels that we have not met the requirements of UK Immigration Rules, paragraph 290 (iii) which is "each of the parties intends to live permanently with each other as his or her spouse......"

Other than sending additional proof comprising of reception booking, cake quote, invites done what else can I do?