What can I do if my brother has taken my mother’s life savings?

They may take legal action against your brother. He must have had Power Of Attorney (or the equivalent in the UK). Taking her government pension would likely be a crime. I'm sorry you have to go through this, because it's going to be bad for your brother. In the US, there would be questions about where the money went, and an elder law attorney may be needed to straighten it out.
Take care. I hope your mother gets the care she needs. That's the important thing here.
Carol

He had to have had POA and if so, they will investigate every penny. They just did that with my mother. Unless he was authorized to cash her pension checks he can be prosecuted.

One clause to check in your parent's POA document is regarding 'reporting of transactions'. My mother actually WAIVED the REQUIREMENT that the POA has to legally make reports of how her money was handled. So, her POA (my sister) doesn't have to account FOR ANYTHING.

I think the clause is something like this: Any provision in the power of attorney waiving or requiring the rendering of inventories and accounts shall govern, and a power of attorney that waives the requirement to file inventories and accounts need not be filed with the clerk of superior court.

I think this is commonly done by parents who implicitly trust their adult children, however this opens the opportunity for elder fraud no matter who is the POA.