I've done it while working full-time but it was much harder than I imagined, and I wouldn't recommend doing what I did.
It is quite practical to do the written exams by distance learning while working full time, using some annual leave to do the (compulsary) brush-up course before taking the exams at Gatwick; more days off work for these.
The hard part, in my experience, is the flying training. I would recommend anyone to try and do this full time, i.e. 4 or at most 5 days a week and then 2 or 3 days off each week to recover. I couldn't do this because I was running my own very-demanding business, so I found a training organisation who could train me Friday, Sat, Sun, and Monday each week. They were very accomodating, but I underestimated my stamina and the strain of the training. I was finishing in the office Thursday afternoon, driving 200+ miles to Bournemouth and staying in a B&B, then starting flying training at 0800 on the Friday, ditto Sat, Sun, and Monday, and then driving 200+ miles home on Monday night. This left me Tues, Wed and Thursday each week to do a full weeks work in the office. After 3 weeks I didn't know whether I was coming or going and I'm sure it cost me more doing it this way, rather than full-time, but I had no choice.
Now that I have got it, it has opened up all sorts of benefits that I never imagined. You often find you are invited along on trips and get to fly nice aircraft, so the owner has a better chance of making it back on schedule, and without it, we would sometimes have been stuck for days.
If you have any more questions, send me a private message.
Go for it, and good luck !!