If you are applying for split year treatment you will need to complete a tax return.
If you qualify for split year then you only report any foreign income for the UK part of the year
RDRM12000 - Residence: The SRT: Split year treatment: Contents
If you do not qualify then you will need to report all your foreign income to the UK.
Tax on foreign income
The guidance at RDRM12150 at www.gov.uk will help you work out if split year treatment applies.
RDRM12150 - Residence: The SRT: Split year treatment: Case 4: Starting to have a home in the UK only