Instead of swapping, how about sharing? I share a half plot with friends, and under the agreement with the council, if either of us decides to give up, the other will automatically have the whole plot (well, that was the original agreement before the waiting list and a whole load of new rules appeared, such as maximum plot space per household came into force.)
As for ploughing/clearing off the turf .... hmmmmm, I wouldn't count on it but if it is a new site, they may just do it the once. On my site, if a plot had been vacant for a while, the council offer to "clear" the plot but usually means a tractor that does more damage to the soil structure, grinds in any broken glass and nicely disperses a load of nightmare perennial weeds, and all in their timetable which could be up to 6 months of the offer
It would be a shame for the only decent top soil to be scraped off and then having to spend a fortune on repairing the damage. I personally would recommend virgin plots - my half plot had been cultivated on continuously for over 50 years and is a nightmare of pests and diseases, whereas the big plot had been one of the first plots abandoned when allotmenteering started to lose popularity because of its location, yet my first year's crops were a great success.