I have heard of a few 20lb+ lambs this year, too and a few of our singles have been very very large indeed. We tried to weigh one very large one. I found the spring weighing thingy, BH brought out a carrier bag to put the lamb in! Well you can't argue with BH, amazingly he did get the lamb into the carrier bag and supported it while I got the hook through the handles. Between the handles giving way, me being unable to hold up the weight of this large lamb as all its weight came to bear on my one hand holding up the spring thingy, so I was following the whole package down as BH tried to give me the weight, and also me needing a little bit of distance from the scale to read the weight (I think I may have mentioned my advancing years...) but not so much I couldn't make out the figures...
There was a lot of laughter, a lamb in a carrier bag on the floor in a heap (don't worry he only freefell the last inch or three) and all I can tell you (and BH) is that the lamb definitely weighed more than 18lbs; that was the last glimpse I had of the scale as the whole lot hurtled away from me earhwards and the spring leapt back to 0!
I did wonder as we were piling the hay and cake into them through all the severe weather and beyond whether we may get oversize lambs. I guess everyone has had to feed more through this winter, and maybe that's how come there are a few of these giants about. Thankfully we haven't (so far, we're onto the hoggs and shearlings now) had any so large they couldn't get born apart from one of these monsters that was dead and the vet felt a caesarian would be the best choice. Both she and one other had a dead monster plus another good-sized lamb - in both cases the vet attended and couldnot believe there was another inside after getting the huge dead one out. Combined weight would certainly have been in excess of 30lbs - but too macabre to weigh, so we didn't.