Thank you. You are correct that if you have been continuously employed at your place of work for less than 2 years then your employment rights will unfortunately be somewhat limited. Most importantly, you will not be protected against unfair dismissal. This means that your employer can dismiss you for more or less any reason, and without following a fair procedure, as long as their decision is not based on discriminatory grounds (i.e. because of gender, race, religion, age, a disability, sexual orientation, etc.) or because you were trying to assert any of your statutory rights (e.g. requesting maternity/paternity leave, etc.).
So even if you had done absolutely nothing wrong, they can still dismiss you in the circumstances. They have given you an option of leaving voluntarily and getting a good reference. Whilst I would disagree that the allegations are serious enough t amount to fraud, it is a potential form of misconduct. So whilst mentioning fraud would be harsh, that would not prevent them from forcing you to leave.
If they are adamant that one way or another you are leaving and you have tried negotiating with them to no avail, then it may be best to just leave before being pushed and getting a reference which you can use to help you with fining a new job.
I hope this has answered your query. I would be grateful if you could please take a second to leave a positive rating by selecting 3, 4 or 5 stars - this is an important part of our process and recognises the time I have spent assisting you. If you still need me to clarify anything else, please get back to me on here and I will assist further as best as I can. Thank you