I need some help please:

My K1 visa has been approved and passport returned to me, and my house has now sold. I have booked plane tickets for myself and the dog to leave in 36 days time.

Who do I need to inform in the UK? I assume it can't be just council tax?

List of what to do and when about Moving : British Expat Wiki

I didn't see mentioned on here, but be sure to fill out a P85 if you've been working. You might be able to get a refund.

Also congratulations on your visa!

When I left the UK I informed the tax credit people, but they just carried on paying money into my account. About a year later they sent me a demand for repayment. Just something to bear in mind...

Definitely file a P85 and also purge your finances of things that could be toxic for US taxation. So if you intend to pay off a mortgage or sell a house do it before you move and and sell investments held outside of pension plans.

Probably not the best way, but i just got up and left - cancelled all accounts & claimed a tax refund online a year later - had it sent to my dad instead and that was it

And if you want to move your pension plan, do that before your leave.

That is, move a pension within the UK.

Think carefully about whether you need to continue a UK bank account. It will be just about impossible to open one when you are resident in the USA.

I changed my bank account to a non interest baring account with no fees. Got all but £2 in there.

Thank you for your replies all. It's been a great help.
15 days until I get on the plane!