Oh bless you Sam, that's really kind.
I managed to aquire a trap and have packed Sundae's mum off with it and instructions on how to use it.
There was some positive news. A man we saw on our travels who lives right behind said he'd heard a really unusual cat cry in the night. He said he hears cat fights all the time but this was different. That completely adds up as Sundae has a blood-curdling miow and sounds like he's in great pain when all he wants is a snuggle. I did an impression and he said "yes, that's exactlly it" so it seems that Sundae has found his way to directly benind his house but can't get back in the garden.
I feel really positive that he'll be found but I'm so sad for his mum who totally blames herself.
All your positive vibes please!