You can still hold the deposit yourself, but you will need to join one of the insurance schemes which will guarantee the deposit in the event of a dispute. Most LL's I would guess are joining one of the free schemes.
If you are going to take a deposit then you will need to join one of these schemes, either an insurance one or one where you hand over the deposit.
As most tenancies are for 6 months, its just coming up to the time now when we'll see how efficiently these schemes work.