Sounds like this is a classic slip and trip. I cannot say if there is any liability here but it would be worth taking some advice. I have seen a case where someone hit a gate on their bike which wasnt painted bright yellow, so who knows.
I would suggest the person involved check their house insurance to see if they have legal expenses cover. If not, do a search round the local area to see if there are any specialists. The chances of no win no fee are slight these days, but there are still some people in the market - although it normally involves a ATE insurance policy (which can be expensive).
Take some advice.