Thanks Guys
Peanut: did you mean remove the 11 t sprocket, and add the 27 t sprocket to make it 12-27? Is that an easy job mate? I dont have much experience with bike mechanics, but I am pretty good with my hands (oo errr).
Dustbowlrefugee: I have a full Ultegra groupset, other than the 105 rear cassette. Having looked on the web I think that shimano rear derailleurs can handle upto a 27 t sprocket.
Buddah: Hesiers Hill did seem pretty steep the other night! I drove up it in the car a few days later and thought to my self, your having a laugh! I will try it out the other way round like you say, going down Hesiers Hill then up Beddlestead lane, which is less of an incline over a longer distance (2 miles).
I can manage that short-sharp dip/hill on Church Lane ok. I had thought about doing that part the the other way around. as you say, its a longer climb.