Just to let y'all know. I bit the bullet and bought the sender spotted by Rememo on ebay. Took tank off today and fitted it. Bingo! All works properly again.
It's not that simple a job though. You have to upend the tank once off and remove the bottom cover. Once that is free the sender needs disconnecting before you can remove the pump/filter unit. Then you need to unclip the old sender inside the tank. You need a torch(flashlight) to see how it's attached then you need to get your hand inside to unclip the sender working blind. After about 5 mins I got it off. I must say, it looked undamaged and exactly the same as the new one. I wasn't 100% confident it was going to do the trick but it did.
As a bonus while the tank was off I ran a fused feed from the battery under the tank and fitted my Satnav socket. Both jobs done in 2-3 hours.