It's not on the DVLA database so presumably either scrapped, exported or possibly racing somewhere. Or I suppose it could be registered with a personal plate ?
For anyone interested, this website is a labour of love by someone who has documented all cars in the Avengers episodes, complete with screen shots;
https://www.dissolute.com.au/the-avengers-tv-series/cars/ It's described as a 1968 pre-production 54, older door handles and without the indicators above the front bumper. If it was a development car from Lotus then I suppose it could easily have been scrapped or ended up racing.
Brian