What do you mean by "We have a grant to help the running of the group."? Is this just a line in the Council's budget, or is a payment made? Your financial regulations probably require all sums received to be banked, so the donations you collect should go straight to the RFO/Clerk to be recorded and banked. If the items you purchase are always approved by the Parish Council, they could also be purchased by the Council in the usual way, presumably by the Clerk. It would be very unusual for a committee of the Council to have a separate bank account, although perhaps with full delegated authority, this might be permissible. It would cause extra work for minimal benefit, so it's not to be recommended.