Forward Parking into a Bay
Forward parking into a bay is an exercise that you may need to carry out on your driving test. In reality however, wherever possible I would recommend that you do not put yourself into a position where you need to reverse out of a bay. Your view is likely to be limited and you are more likely to put other people at risk. Especially in a busy car park where vulnerable pedestrians and children could be behind you.
If you need to do this, choose a bay with plenty of space around it. Where there are cars parked on either side, you will find it more difficult to enter the space. You will probably have to stop and adjust your position.

If this is unavoidable, you should approach the space from a wide position. This will lessen the amount of steering involved (see diagram). This may mean having to steer away from the bay on the approach to give yourself room. Make sure that you are fully aware of what is behind and around you, and position early to avoid suddenly swinging out.
Once you start to turn in, if you are not quite sure that you have enough clearance, stop and reverse a little to adjust. Check behind over both shoulders before you do this to ensure it is safe.
Reversing Out of the Bay
If you have cars alongside you when you reverse out of the bay, then you may have to reverse in a straight line until you are clear. But when there is clear space, you can steer as soon as you begin to reverse. It does not matter if the front of your car swings over the white lines.
An important point to note. Car parks sometimes have one-way systems. Make sure you know which way to go!
Once again, safe observation is paramount. You are much more likely to get in other people’s way when reversing out of the bay, than you would when reversing in. You need to continuously look all around and show courtesy to those around you. Always be ready to stop and allow drivers; and particularly pedestrians to pass before you continue.