The UK is rolling out Electronic Travel Authorisations (ETA), which will need to be applied for prior to travelling to the UK for nationals of countries who do not require a visa to travel to the UK as a visitor. AN ETA is not a visa but gives clearance to travel to the UK.
An ETA will cost £16 and permits multiple journeys over two years. You can find out more on the official UK government factsheet. You will still be entering the UK on the basis of being a Standard Visitor but it will allow mutiple entries. You are unlikely to receive a stamp in your passport at the border, so you should retain your boarding pass/ticket as evidence of your date of entry.
An ETA is not a visa and does not grant you immigration permission. It simply provides you with authorisation to travel to the UK. When you arrive at the UK border, you are entering as a Standard Visitor. We must verify these each time you enter for teaching, as they only allow for a single entry.
You can apply for your ETA on the UK government website:
Apply for an ETA
How can I show that I have an ETA at enrolment/visa verification?
LSE will not need to see evidence of your ETA at enrolment. However, as you may no longer receive a stamp in your passport, even if you speak to a Border Force Officer, we will need to see a copy of your boarding pass/ticket so that we can see the date that you entered the UK.