An immigration official can deny you entry to the UK at the border, even if you have valid entry clearance. Nationals of certain countries do not require a visa before travelling to the UK and are referred to as non-visa nationals.
The following countries are considered as being non-visa nationals: Australia, Canada, Hong Kong (SAR), Japan, Malaysia, New Zealand, Singapore, South Africa, South Korea and the USA.
Nationals of Kuwait, Oman, Qatar or the United Arab Emirates require an electronic visa waiver or a valid standard visitor visa before entering the UK.
Nationals are still subject to immigration control and can be denied entry by a border officer. Typically, the reason behind this can be:
– Previous issues with your immigration history
-No onward travel plans
-Your leave could be curtailed
-Issues with your travel documents.