Im a South African and my visa will expire 2 days after my arrival in the UK. Is there a grace period or do I need permission before I can even travel? What's the process I have an emergency ?
There is an enabling rule found in Paragraph 31A...
Where a person has arrived in the United Kingdom with leave to enter or remain in the United Kingdom which is in force but was given to him before his arrival, he may apply, on arrival at the port of entry in the United Kingdom, for variation of that leave. An Immigration Officer acting on behalf of the Secretary of State may vary the leave at the port of entry but is not obliged to consider an application for variation made at the port of entry. If an Immigration Officer acting on behalf of the Secretary of State has declined to consider an application for variation of leave at a port of entry but the leave has not been cancelled under paragraph 2A(8) of Schedule 2 to the Immigration Act 1971, the person seeking variation should apply to the Home Office under paragraph 32.
What this means is when you arrive you can explain your predicament to the Immigration Officer who lands you and ask that they exercise Paragraph 31A in your favour. If you are successful, they will extend your visa so that you are not an overstayer.
The important phrase in this rule is "
...is not obliged to consider...". It means they don't have to do it if they don't want to and they don't have to explain themselves.
For your other questions, when you leave the UK as an overstayer, your carrier will turn the info over to UKVI and you will face the consequences in future applications.
The 'grace period' is a 28 day window to leave the UK voluntarily before mandatory bans start to kick in. If you attract a mandatory ban, they will be required to refuse your applications.
The airline will get a large fine if they bring someone to the UK that is not allowed in the UK. Therefore your airline may not allow you to fly regardless of what an Immigration Officer may decides when you try to get past them.
Expect the Immigration Officer to question you, as the computer may flag up the short time left on your visa when they scan your passport.
You may find that the Super Priority Visa service will sort you out before you travel.