I took in a stray 2yrs ago... i have no other cats.
He is really comfortable around me, even playing with my hand and loves my attention but as soon as he hears anything like a bell or squeak he becomes frightened and starts growling like a dog.

He is also comfortable with my family or strangers as long as i am there for reassurance otherwise he will bolt.
If my family let him inside while i'm not around he will not settle.

I recently got him a microchipped toy mouse to play with but it made him jump and he won't let me put a collar on either.

He is such a big strong looking cat to be acting like this and we think hes 5-7yrs old.
We get the impression that he was abused before he came to us... or annoyed by children.

How can we help him?

Some cats are just timid and nothing to do with abuse or children.

My brother in laws cats are all timid and run whenever the family visit .

He lives a quiet life in a quiet place .I could imagine if any of his cats went missing people would think they had been abused when really they have a life of luxury

I agree that some cats are very timid and you just have to preserver with them, my lovely cat which we had from cats protection loves me but hates my other half when he comes into a room she runs, she is terrified of men in general, plus she will only go as far as the back door step and that's its she will not go outside and if you shut the back door on her she cries and scratches the back door.

Well done for providing a loving home to a stray.

From what you have said it seems likely that your cat left his previous home because something happened there that scared him ~ perhaps the arrival of a new baby or a change in the owner's circumstances or the arrival of another pet? He also seems quite sensitive to noise so perhaps he is a victim of Bonfire Night?

If you want your cat to feel less scared of other family members then they need to be more involved in feeding, grooming, playing etc with him. Will he take tasty treats from your hand? If so ask the rest of the family, starting with the person he is least afraid of, to try hand feeding. If he likes to be stroked, can other family members try to touch him? Does he sit on your lap? If so could another family member wear an item of your clothing with your scent on it?

Also make sure all members of your house are quiet & slow moving around your cat. They should not make direct eye contact with him, but just glance at him using slow blinks. This is a non-threatening signal to cats & may help alleviate his wariness of other people.

I can recommend the books by the feline behaviourist, Vicky Halls if you want to know more about cat behaviour & how to deal with fears, phobias & timid cats.

Good luck.