The Acas Code of Practice on Discipline and Grievance Procedures (PDF, 167KB) indicates that criminal charges or convictions outside employment should not be treated as automatic reasons for dismissal.
The main consideration should be whether the offence is one that makes you unsuitable for your type of work. Your employer, having considered the facts, will need to consider whether your conduct is sufficiently serious to warrant disciplinary proceedings, including dismissal. The Acas Code goes on to say that workers should not be dismissed solely because a charge against them is pending, or because they are absent as a result of being in custody. So the fact that you have been accused of a criminal offence should not necessarily affect your job.
What your employer should consider is the nature of the alleged criminal offence and whether it affects your ability to carry out your duties. If, for example, you have been accused of fraudulently obtaining money and you work in the accounts department handling cash on a daily basis, this might give your employer grounds for taking action.
There is no legal requirement for your employer to await the outcome of any criminal proceedings before taking any disciplinary action, including dismissal. It all depends on the circumstances of each individual case.
If you are worried, you can contact one of the charities that support people affected by criminal convictions at work such as theInformationHub provided by charity Unlock or NACRO. Both charities run confidential helplines.