What will happen to me if I have been arrested for depoisting fake1 pound coins into my bank.

Really depends if you did this knowingly.

Hello:

If you did it in America, you'd go to jail for a while.

excon

Assuming they can show you where in full knowledge of the fact the currency in question was indeed a forgery.

So attempting to deposit several bags of funny money WILL get you into serious trouble.
They would NOT arrest you if it was 1 or 2 and an honest mistake.

There's clearly more to this than the OP has mentioned, but I bet we don't get the full story.