I often get enquiries from people who are currently expats and are planning to return to the UK.
Typically as an expatriate, you will have had very little contact with HMRC over the past years or you may have UK rental income from property and needed to file tax returns to declare this income.
You'll normally have your non-residence status but be concerned about telling HMRC that you have arrived back, about possible capital gains tax issues and general concerns that thing may have changed and you need advice to make sure that you come back considering tax advantageous options.
When you arrive back to the UK with the intention of remaining for the foreseeable future, HMRC will normally consider your fully UK resident from the date that you arrive. This means splitting the tax year into two parts and taxing each part as non-resident and resident respectively.
It is important to note that this splitting is not legislated in law but a concession and this means that HMRC could if they please, argue that you are resident for the entire tax year. This may cause issues with foreign income, gains or earnings so I suggest if you can to time your return to Great Britain as soon after 6 April as possible. This minimises the scope for retrospective changes by HMRC at a later date.
Sometimes you may be returning to the UK for just a short time and if this is typically less than 2-3 years then you may be eligible to remain non ordinarily resident. This is a special case that may be of use to you if you will be back in the UK for a short time and you still have foreign income you would like not to be taxed.
Often HMRC loses track of your records when you have been away and so when you return they may ask you to complete forms to establish where you have been, what you have been doing and what income you may have had and especially from the UK.
Each of my client situations are different and there are almost always some interesting opportunities to come back to the UK on a certain basis and with the foresight of good advice. This helps you plan your return better and reduces surprises and uncertainty.