The Reform campaign office on Cardiff Road in Caerphilly.As voters go to the polls in Caerphilly today, they will not just be electing the seat’s new member of the Welsh Parliament.The result, when it is announced in the early hours of Friday morning, will also give a clear indication of where British politics as a whole could be heading next May.The south Wales seat has been a Labour stronghold at both Westminster and Cardiff Bay for decades, with tellers advised to weigh rather than count the party’s votes.At the last Senedd election in 2021, Labour’s Hefin David won with a majority of 5,078 over Plaid Cymru’s Delyth Jewell. The Reform UK candidate, Tim Price, came seventh with just 495 votes.This time around, however, the result will be very different.The by-election is being held following Hefin David’s death in August and opinion polls suggest the seat is a straight shootout between Reform’s Llyr Powell and Plaid’s Lindsay Whittle. Labour’s Richard Tunnicliffe is expected to trail in a distant third.The significance of that result cannot be overstated. No party other than Labour has ever held the seat since the start of Welsh devolution in 1999.At Westminster, the seat has been in Labour’s hands since 1918 (ap