BP Solar System

Is there a fuse or breaker unit in the regulator to battery line. It may have opened, or, perhaps a screw fixing for the cabling in the regulator has been left loose and is now NOT contacting and passing current. Check both the Positive AND negative cabling for continuity.
Most if not all regs, switch/modulate the negative line to control battery charge flows.

Can you fit alternative temporary cables to the reg and feed them to battery to check circuitry is ok or not, ie, if it works with an alternative cable set then there must be a fault in the two conductors feeding the battery.

Thanks for the advice, we bought the van with the solar system on it second hand, it was supposed to be working! Will give your suggestions a try and see how we go. Thanks again :)