"...3rd lane, overtaking lane, BUT I could be wrong!!!!"
ALL lanes other than the nearside lane are overtaking lanes.
"I drive fairly close to the speed limit so I figure the slow coaches can stay left and the speedsters can pass me in the right hand lane. "
Hopefully, then, Brinjal, your inconsiderate driving will, before it inconveniences too many more people, be pointed out to you by a traffic officer. He or she may simply point out the error of your ways or may just issue you with a fixed penalty notice which will cost you £100 and three points:
http://www.bbc.co.uk/news/business-22770064