Can you arrive in the UK before your UK visa start date
According to Home Office guidance, to activate your UK visa you need to arrive in the UK within the visa validity and not before the visa start date.
What happens if you come to the UK before your UK visa start date
If you were granted UK work visa (e.g. skilled worker) or UK study visa, and you come to the UK before the visa start date, you may be allowed to enter as a visitor if you are a visa free national. If you are a visa national you cannot rely on visa free entry as a visitor. Anyone who is not on the list of visa nationals is normally visa free for visitor purposes to the UK.
Allowing entry as visitor will depend on the immigration officer at the border who will assess if you meet the visitor criteria. If you area allowed in, you will have to leave the UK and re-enter to activate your work or study visa.
Home Office guidance on entry before visa start date
The sponsor guidance for workers and students states as follows: ‘You must check the worker entered the UK during the validity period of their visa. If they entered before the ‘valid from’ date on their visa, they will not have permission to work for you. If this happens, you should advise the worker to leave the Common Travel Area (UK, Guernsey, Jersey, Isle of Man and Ireland) and re-enter the UK once their visa becomes valid.’
As a general rule, the earliest you should arrive in the UK is the date your UK visa becomes valid.