I'm surprised your Lotus has the correct dropouts to even think of doing such a thing. I have an 87 Elite 600 Lotus that has dropouts without little adjustability for chain tension. I ended up buying a 1974 Koko 3000 complete bike that I stripped and bought a new rear wheel for a fixed conversion. It ended up being pricer than I was hoping for(about $140 just to get it Fixed gear rideable) and then I spent another $200 doing stupid things to it like putting Brooks stuff all over it(although admittedly it looks pretty sweet!)
I wouldn't convert a sweet stock bike to SS/Fixed, there are plenty of good frames out there that you could do that too. But I am a Lotus fan anyways, so unless I found a Lotus high end frame with nothing original on it, I wouldn't convert it to start with.
BUT like I said....you might wanna be sure your dropouts will work as fixed/SS anyways. My Lotus wouldn't even if I wanted to.