In reply to philpaynter: I started in Jiri not Lukla. Most people fly to Lukla as it is the nearest point you can fly to so speeds up the whole process.
But, you can get a bus from Kathmandu to Jiri and start walking from there. The advantage of this is that you get match fit at lower altitude and also aclimatise more slowly. The "pre lukla" walk is lovely and very quiet and is also where the lads set off from when they did the first succesful attempt on Everest.
Ignore all of this if time is an issue though as it will add 7 days walking to get to Lukla. (but does avoid an air fare)
Also, if you are lucky enough to have time, do explore the other valleys once you have walked to Gorak Shep, you can return to Dingboche and then walk toawrds Island peak along the Chukung Valley which is spectacular and for my money the best view from Chukung peak (Ama Dablam and Lhotse). You can also do the Gokyo Lakes as well. To do all of this will take a considerable amount of time if you don't want to rush it and enjoy it. I would guestimate at least 4 weeks, but would say 5 weeks to aclimatize and enjoy it.
You will be pretty fit on your return to UK!