Thanks for the rapid replies: the first few are informative and confirmed my understanding, the latter becoming more aggressive, so I'll cut this off before it gets into a slanging match.
I'm entirely sanguine with the resolution I have achieved this evening and the earlier responses to this post. I wasn't unrealistically expecting a magic wand to be waved to recompense me for my woes, simply asking this forum whether any folks had any experience or guidance that could be of use to me. Exactly the process that allowed me to get the family to California and back in Aug in CW for £3.5k, for which I am grateful to FT and its users.
I spent about 2 months on this forum planning the trip and, despite careful planning, have come a cropper, mainly due to my optimism on the RTB leg (I had a secondary and tertiary plan involving car ferries and an overnight drive on the way out!). Every day is a school day and I hope that other, less experienced FT'ers, read this and learn the salutary lesson of the knock-on effect of operational/or any other delays.
The extra spend this evening has cost me roughly the same as I saved when I hedged my £:US$ rate on the evening of the Brexit referendum, one of my more inspired
moments, so it's all swings and roundabouts but I'm still several £000 up.
Thanks for the positive replies.