Hi Its MamaTax Here!
Thanks for the question.
If you are moving to UK permanently then you become a UK tax resident as well and taxable on your worldwide income in UK. However UK has a Double Tax agreement with US - so if some of your income taxed at source in US,then no further tax will apply in UK.
To register for self assessment you need to notify HMRC (UK tax office) and they will send you a Unique Tax Reference (UTR) and tax returns at end of tax year for you to file your tax returns.
To notify HMRC please call this number 0300(NNN) NNN-NNNNand ask for self assessment registration.
If you are stuck on filing the return, this site is very helpful in telling how to go about the filing the form. Alternatively you can get your tax return filled with a local tax expert for as little as £50 by posting your requirements on sites like uktaxadvisors.com or findukadviors.co.uk or several other sites.
Hope this helps.
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I see you are offline so i will log off and wait to hear from you. Thanks once again.