London has a strong contract market particularly in financial services. I've done almost ten years and never struggled to Go from one contract directly to the next. If you are good And realistically priced then you'll be fine for work.
Get your first contract and be stingy with your money until you have 3-6 months savings built up, then you will be fine.
In all but the tier 1 investment banks contractors are not expected to work long hours. They ARE expected to be good, though realistically there are a lot of rubbish ones out there. They tend to be the ones spending six months out of work. Good people rarely do.
I work at the senior end of programme manager, often directly reporting to a CxO or one of their direct reports. The standards are demanding but I take 6-8 weeks holiday a year, don't work weekends, don't work very late, don't travel much, don't stress. Be decisive, don't daff about and you'll get more done in 25-30 hours a week than most perms do in a month