Hello and thank you for your question. I will be very pleased to assist you. I'm a practicing lawyer in England with over 10 years experience.
If your mother were to pass away leaving a will in terms you suspect you could enter a caveat to prevent probate being obtained and seek to challenge the will on the grounds of lack of knowledge and approval of the contents on the part of your mother. Alternatively you could seek a claim under the Inheritance Act for reasonable financial provision which claim would require that you lift the caveat and allow an application for probate to take place making a claim within 6 months of the issue of a grant of probate.
In any event a caveat will give you some breathing space and allow you to negotiate and fact find
You can enter a caveat using a specific form or alternatively just by sending the required information to any probate registry with a fee (from memory the fee is £13). The information you must provide is as follows:
a signed request, asking for a caveat to be entered
the full name and date of death of the deceased, as recorded in the register of deaths, (in addition, you may also give any other names used by the deceased).
the last permanent address of the deceased.
your own name and address. This is the address to which any papers or correspondence relating to the caveat will be sent or served upon you. This must be an address in England and Wales.