RDRM10610 - Residence: General Information: Counting days
Residence is not purely a matter of day counting. The number of days spent in the UK is one factor which needs to be considered alongside others.
When you are counting the number of days an individual has been present in the UK during a tax year you must include all of the days in which they have been in the UK at the end of day (that is, midnight), remembering that February has 29 days in a leap year.
Note: that the days of arrival in and departure from the UK for each visit up to 5 April 2008 are ignored (refer to EIM42840).
For example
An individual arrives in the UK on 10 June and depart on 12 June. This would be counted as 1 day if it occurred up to 5 April 2008, but would count as 2 days if it occurred from 6 April 2008.
Remember that there are different rules for counting days for the 100% foreign earnings deduction (refer to RDRM10615). In those cases the day of arrival is counted and the day of departure is ignored. Be careful not to mix up the two [refer to EIM40106].
For all taxation purposes the territorial sea is part of the UK. Days spent in UK territorial water; that is within the 12 mile limit, are days spent in the UK [refer to EIM67105 and EIM67110].