accident in shop kick started a flare up

I agree with your friends you should ask fo4 more It should never have happened in the first place. .

While things are different in the UK vs the US for slip/fall injuries and tort law, I think morality is universal.  You have a pre-existing condition, but if their negligence caused you permanent damage, then you have a right to be compensated for that injury.  But, with C.S., you wont know for a few weeks yet, if the damage is permanent and has worsened your condition, or if it has just caused a flare up.  So, I would not sign anything yet; I would wait and see, and if they call and ask how you are, avoid the normal "I'm fine, thank you" that is so common to say, as it implies you are better.  If the flare up goes away and this singular incident did no harm then your injuries are more limited.   A few years ago, my daughter and I got food poisoning at a nice Italian restaurant.  She was immediately ill, and I got ill the next day, for 3 painful days of salmonella poisoning.  The restaurant denied the problem, so I called the health inspectors out and they found the issue - it was a faulty refrigerator that stored their salmon, so we ainted tainted meat late at night.   They pain for all my meds, my daughters meds, my doctor visit and a few hundred to each of us for pain and suffering.   The amount worked out to be $750 US.  I never took them to court and I thought the amount was fair.  Others would have sued them for thousands of dollars.