Can i stop my brother he has power of attorney over my mother?

hi my mum is 88 years old and is in poor health.she has emphysema and very poor balance .she has a trolley to use but she has to keep hold of the trolley when she is trying to do anything.like making herself hot Drinks this. could be dangerous i contacted the occupational therapist and they said they had a team of people someone would go and see my mum to offer her the help she needs .but last night i got a phone call from my brother telling methat he had power of attorney over mu mum he has had this for 16 years and me and my sisters knew nothing about it ..he has told me to tell the ot to contact him .but he is going to cancel everything i have tried to do .he said that if we interfered again he would contact his solicitor to stop us .this has come as a shock to us is there anything i can do .i would be very grate full for your HELP thankue sheila.i live in the uk