A description species over my garden

I don't have a good record on submitting descriptions to rarities committees. I avoid this process mainly by not discovering birds that require descriptions to be submitted for 'acceptance'. And should I accidentally stumble upon a 'description species' I avoid it by not bothering submitting. 

I did submit a description once, many decades ago. It was a Red-Necked Grebe in Scarborough Harbour. In winter. And it was rejected because it might have been a Slavonian Grebe. Which it massively patently wasn't. Because if it had been a Slavonian Grebe, then obviously I'd have titled the description 'Slavonian Grebe'.

Anyway, forward several decades, and I was sat in my garden early one evening peering up into a blue sky looking through my Leica 8x42s at House Martins when I glanced around and saw a large bird flying towards my garden from the south. It passed by at what I would call a middling height in that it was neither a speck in the firmament nor grazing the top of the Leylandii, and took a line a couple of houses to the East so I could get a side-on view of the bird. I duly submitted my record to the Herts bird club site (and thence on to Birdguides ! WooHoo!), and then received an email requesting a description. Oh.

So here goes. It was big, in that it was Goose/Cormorant/Heron size. It was thin, long neck, thin wings, longish tail, like a flying crucifix. It was mainly white, with a bit of black on the wing, and a vaguely recall a scrappy blackish tail with an odd feather, like it was moulting. It was taking regular quick quite shallow flaps. It was in a hurry.

Taken by complete surprise at this bird belting over my garden I looked at the head, and, yes, as you have probably worked out by now, it was a Gannet. It had a Gannet's head. That long ivory bill, big eye close to the bill, pale buff mass of stuff round the base of the bill and those black lines giving the distinctive Gannet Trim all around. I didn't look at much else to be honest, given that I was aware that for a few seconds I was looking at a sight I was never going to see again and that that beguiling head is the stand-out feature IMHO. 

So now I have to fill in a form that will convince others that it was a Gannet. How do I do that? Get my Field guide and copy down the relevant bits that make it look like I carefully studied every feature and made a note? Or just say it was a Gannet. With a head like a Gannet's?

If it gets rejected, what will be the confusion species? Great White Egret? Heron? Juvenile Cormorant? Swan?

Anyway, here goes. Wish me luck.