When can i use all the money in bank account after a cheque has been cleared?

I cashed a £400 cheque to a Natwest branch on monday. On wednesday i saw the amount in my bank account had risen to £600 but said i could only withdraw £200. Can i still by the new £599 iPhone with the money in my bank account or do i have to wait until the cash point says i can withdraw the full £600

Difficult one, in truth you should not write the cheque (legally) until the funds are available, even if the cheque may not be banked for a few days, when the funds will be available.

If you do not have an overdraft facility, your going to have to wait until it is cleared.

If you go to the counter you can draw as much as in your account. The machines restrict the amount so they don't have to fill them with so much cash. Thats all. Did you have £200 in your a/c when you paid the cheque in? If you did the full £600 is yours and you can use a debit card to buy the camera.
On the other hand the £200 was some kind of overdraft you are going to check if you can use it.
@ EDIT There's no way any shop is going to accept a cheque for £599 LOL There used to be cheque cards that guarnteed your cheque, but that was only up to £100. Modern debit cards have taken their place that comes out of your a/c on the spot. Get one if you haven't got one.

A cheque takes 4 working days to clear from the day is put in the account, so it depends when Natwest actually put it in (i.e.did you do it at the counter or at a machine- They may not put it in that day).

The reason you saw 600 but could only take 200 is because the cheque hadn't cleared yet. As soon as it says 600 you'll be safe to use the funds.

Be cautious though! Even after you have the funds, the cheque can be reversed if the person who gave you it doesn't have the money. This means you could spend the money and the bank can suddenly put you overdrawn.