My initial troubleshooting of the high SWR on the HF antenna has eliminated the EFHW/balun as the cause and also the antenna switch and lightning arrestor. After futzing around it seems to be a fault in the cable from my shack at the front of the house to the antenna in the backyard. I need to do some more checks to ensure this is the case (e.g. not just a connector on the cable). It is a direct bury cable so won’t be fun to replace.