I would check with HMRC.
Both the questioner and her husband will need to complete form P86 - arrival in the UK. These get sent to HMRC.
They woud then both have to file UK returns. The questioner has a domicile of origin within the UK so would always have to report worldwide income & gains on a UK tax return from the date she becomes UK resident.
The husband is not UK domiciled so could file claiming the remittance basis if this produced a lower tax bill than filing reporting worldwide income & gains.
They would continue to both report worldwide income & gains in the US on the US returns -albeit that some US source income might arguably have to be resourced as foreign source on the US return if double taxation is to be avoided.
Yes I know I am typing in tax jargon. This is deliberate because the tax situation is about to become much, much more complicated. Using the right words will make it much easier to search on Google & learn what the rules actually mean.
