R.R.
Hi Molly-
We took our daughter to Australia when she was 15 months- so I hear your worry!!
But to be honest, it worked out just fine!!!
The time zone (they're 17 hours ahead!) was difficult and she went back to taking 2 naps (she was down to 1 afternoon nap a day) while there.
I'd just 'wing it' and deal with the issues as they arise.
Try to keep him up and get him on to UK time, but don't force it too much... Chances are you will be up in the middle of the night! Our experience- our daughter was up around 4 am most mornings!!! In some ways- it make the trip seem EXTRA long that way!
As for the flight- We did use some benadryl for the plane rides- and spoke to our ped. about it in advance! It just helped her fall asleep easier on the plane.
Other advice- pack extra outfit for everyone- my daughter's diaper leaked while i was holding her and I had a huge mess on my shirt!
And be smart about what you dress him in- we choose an outfit with a ton of snaps up the legs- not a good idea for when needing to change while in your seat (which we had to do during take off- bc of course she had a BM but we couldn't leave the seats!)
Pack lots of snacks- and something for their ears (pressure) during take off and landings... (We used a paci)
Although he is a little young, we went to a $1 store and bought new toys- that we then left with our cousins in Oz! This kept her interested...
Otherwise, on the trip home I do remember just walking the aisles with her. Luckily the passangers were friendly and understanding.... In all, the plane rides themselves were the easiest part of the whole trip! As we learned, a vacation with kids isn't a vacation- just a relocation! :)
(but it does make for fond memories!!)
Good Luck!
(ps- we also found some good blogs people had written about advice for traveling with kids.... don't recall any specific ones, but it was good to hear about peoples successes and learn from mistakes!)