Probate and Pension Credit

[210640jm]

My mum died late july 2006 leaving approx. �18K with no will. The sum left was split over 4 bank accounts, 3 of which paid up without any problems. The 4th account was with the Post Office who insisted that because the account had more than �5K in it we had to get probate for them to release the money. After consulting a solicitor probate was granted without any problem. However she took it on herself to contact the Pension Credit office to see if mum owed them any money. Because of this we have had to freeze the cash until they give a reply. Mum declared all savings on applying for Pension Credit but her Pension paid into her bank during her illness at the end of her life added to her bank account total. Pension Credit are now asking for Bank statements from when mum applied for it. Has anyone had this problem and if so, how long is it likely to take for them to decide if mum owes them anything or not? Is there a time limit or can they drag it on to suit themselves?