The John Allerton float rod is 18/20ft and is made by Tri-cast. It costs £360 odd and you won't get much off. Fished the Shannon last week with one and can remmend it if you can afford one. The only long rod that betters it is made by Carbotec and that costs a whpooing £600!
Paul is right, sadly the Carbotec's are no longer made - cracking rods though if you can get your hands on one!
Lennart,
Maybe take a look on e-bay, but keep an eye out for the M.A.P. 20 ft rods. Very nice action, spliced tip and not too heavy either. I have the 15' and the 20' and used them a lot in Norway and Sweden on some of those deep rivers.
Try the Daiwa Spectron 17/20. Slightly better then the original Tri-Cast Allerton 20ft'er.I've got both & have caught loads of fish with them on the lower Aire @ Beal/Birkin.If anyone wants to buy the Allerton it's for sale @ £120,if you want to give me a call on 07729920170.There's also a handle which converts it to a very nice 16 ft'er.But it will be december before I can sort it as I'm just off on holiday.