when you choose newcastle both Owen and Martins have clauses in there contract however in my season with arsenal there is no such thing! can anyone explain?

Probably the same thing that I did when I was Newcastle manager. Made sure the first thing I did was give them new contracts getting rid of the clause.

Could be one of 2 things:

1) Your scouting isn't good enough to "know" about these clauses.

2) The AI got rid of them ASAP.

I think I read somewhere else they were hidden release clauses although I cant remember what they were.

they are indeed hidden clauses. they are in the contract, but they just dont display when you scout them...

I think it depends what the clauses were. If it is a buy back clause normally only the team who it it with can see it. But if its a minimum release fee i believed that everyone can see it.

not sure it was when i first started and checked straight away so the manager did not have time maybe they are hidden cause newcastle accepted £13m for martins and rejected £12m

Not really true. They can be found out but they do not always show.