The S1 has locking nuts but no key.
Any idea where I can get one or how to get it off?
That looks like an aftermarket one. They’re made of cheese. Find a slightly smaller long socket you’re not particularly attached to and hammer it onto the nut. Then remove.
I have loads of sockets I am not attached too as I don’t know how they work
Sounds like a plan though ta.
I’ve never done on on wheels with such a deep hole. Some accurate swinging of the hammer required. Good luck. 
I have only positive words about these
Steve - looks identical to mine - I think Lotus supplied a number of variants? - I have a spare you are welcome to share - pm me your address or collect?
It is the same design as used on early S1 Elises. The 3 pin positions do vary slightly however, so one key does not fit all sadly.