Thank you, bacon - I feel I know more about fissures than I ever wanted to.
I forgot to say, I thought moist toilet tissue would help, but it really stung. I'm not sure why - reading the packet, citric acid was one of the 'ingredients', but I'm not sure in what concentration, so can't be sure it was the culprit. Anyway, ordinary toilet tissue dampened with tap water was much better and quite soothing.
Other (very blunt) advice I was given includes - what you really want for a fissure to recover is large, soft poos, ideally once or twice a day. So they gently stretch your anus, but won't scratch it.
Laxatives, or laxative effect food taken without bulking agents, just make you do lots of small more 'liquid' poos. Pooing a lot irritates your bowel and anus, and obviously if you are wiping lots of times a day, you're going to irritate the area more. That's why you want to 'soften' and 'bulk up' rather than take a laxative.
Also, lots of small poos might sound like a more bum-friendly experience - but an anus that isn't used to stretching in a relaxed way is much more likely to tear when you do (inevitably) pass a stool which is hard and/or large.
Someone asked if lansinoh might help. I'd be careful if you are dealing with a very open, bleeding fissure, because the main challenge is just keeping it clean - but if a fissure is just 'grumbling', then as a preventative measure, it might not be a bad idea at all. I've been known to use Elizabeth Arden 8 hour cream to soothe some minor scratching (figured it was developed to treat burns, so why not). Lansinoh would certainly be a darn sight cheaper.