First of all thank you all for your comments and tips on how to find Baby.
He's now home safe and well - yey!
I was getting really worried that I would never see him again but yesterday before I had to set out to work I decided to check the field behind my house again. I started walking the edge of the field calling his name. I stopped near a huge patch of bramble and called, as I listened a little cat call came back. You can imagine what my stomach was doing at this point.
Baby hasn't got a definite cat meow so I was half thinking this couldn't be him because it was a clear meow. Anyhow I called again, and again a call came back. I quickly ran around to the house that backed onto the bramble patch and asked if I could call from the garden side.
The night before I'd popped notices through the doors of my neighbours so the lovely lady knew who I was and came to help search.
As we called no call came back and then...another cat jumped up onto the fence and called to us. I was so deflated and disappointed.
I went back around to the field to carry on my search, starting at the point where I had left off. I called and to my excitement the call came back again! And this time the call was followed by Baby's distinctive little half meow and a sneeze! The sneeze confirmed it as from birth he's had a virus caught from his mum which means that he sneezes a lot.
You can imagine how excited I was at this point calling out to him and kung fu kicking the brambles to get to him - I must have looked like a mad woman to anyone looking on. He was trapped in a bramble cage. I grabbed him and held him so tightly he wasn't going anywhere!
As soon as we got home Sweetie checked him out and he tucked into 3 cat food pouches.
It's so good to have him home. Thank you once again.
Now life can get back to normal - phew :)