Programming single-button key - Legacy BP 2005 3.0R

Hi - I'm trying to program a third key for the car, and there are millions of different methods on the internet, none of which seem to work.

I'm sure it'll be simple, but is there a definitive answer please for a UK car?

I also have the two white male/female plug/sockets under the dash.....  do I connect these to put the car into 'program' mode?

Thanks!