If conservative treatment (physio/chiro/excersises) hasn't helped then it's probably time for surgery.
There is no guarantee that surgery will help (speak to the surgeon about likely outcomes and risks) and I often see failed spinal surgery cases (but I wouldn't tend to get the sucessful ones coming to me would I?
)
The only real downside of the fusion (if it helps) is that 10-15 years later you are fairly likely to have osteoarthritic changes at L3/4 and/or L5/S1 because of the extra movement demands through the levels adjacent to the fused level....but cross that bridge when you come to it. Has the prospect of a microdiscectomy been discussed?.....or is the bulge too massive?
Where in S London are you?