"Cable but I needed to connect wireless to see the drive in the first place. So to be honest I'm not sure if I'm honest but loathed to stop it as it's been running so long already"
Suggestion:
When you finally get yourself out of this mess, THROW AWAY Time Machine, download CarbonCopyCloner (absolutely free), and use CCC to do your backups.
You won't be bothered by such problems again!