Whilst the CAB information is correct insofar as what you should do, their heading is misleading.
You cannot withdraw a statement you made as a witness. Once it’s made, it cannot be “unmade”. What you can do is make a second statement saying that the contents of the first were not correct.
If you do this you should be aware of the consequences. The police and the CPS have a number of options if they still wish to proceed with the matter:
1.They may just not use you as a witness. If they have sufficient evidence without your testimony they will still go ahead and it will have no impact on you.
2. If they believe your testimony is vital for them to secure a conviction and they still want to go ahead they will firstly ask you to attend for the trial. If you do not attend they may ask the court to adjourn the trial to a later date and to issue a Witness Summons against you. This means that if you fail to turn up for the later date you can be arrested and brought to court. They do not do this lightly or very often because the CPS is not generally in the business of having reluctant witnesses arrested but it’s important you are aware of this possibility.
3.If, having made a second statement refuting the first and you do attend court (either voluntarily or as a result of a summons) you may face close questioning about the discrepancies between your two statements and the reasons for them.
The course of justice relies very much on witnesses being prepared to attend court and give evidence. Often the very fact that the police have a statement is sufficient to encourage a guilty plea and no trial is necessary. Further down the line many defendants “put their hands up” (plead guilty) on trial day when they learn that the witnesses have attended. At the very least you should postpone your decision until you know (a) whether a prosecution is to take place and (b) whether the defendant has entered a Not Guilty plea. You never know, one day it may be you or yours who are dependent on witnesses in order for you to see justice served.