The criminal investigation by the police and the civil investigation by your employer are two separate things. The lack of a prosecution / conviction in the criminal case does not impact the ability of the employer to take action.
If you are now dismissed, there is not point pursuing the grievance. You have two choices to consider if you are contemplating further action:
Taking your employer to Employment Tribunal for unfair dismissal. Such a case would be based upon the employer failing to follow the correct disciplinary procedure (I�m not sure if it did or not, too little info to say). You could talk to ACAS about your circumstances and see what they say about it.
Suing your employer for wrongful dismissal. This is not the same thing as unfair dismissal and is based upon the employer breaching the terms of the contract. It is possible to do this at ET, or County Court. This would be based upon them not giving you notice, or money in lieu, unless they are claiming that gross misconduct was the cause of your dismissal � in which case you get no notice. Goodness only knows why it took 3 months to investigate - that�s just typical of public sector and not-for-profit organisations. Wrongful dismissal will only get you your notice money.
What outcome were you looking for?