If that is his sole income, then it is way below the tax threshold and he should have been reclaiming the tax on the interest. If his income was below £17,000 then he can fill in form R60 and reclaim four years of tax on the interest. From April 16, the first £1,000 interest is tax-free and no tax will have been deducted by the bank.
He could move the money to higher paying current accounts, as long as he has enough transactions on the accounts. That might mean having two accounts and setting up automatic payments between the two to meet the transaction rules. Google the MSE Forum and you will find plenty of threads on how to do this.
Although he is retired, he can still make payments into a pension and get a tax uplift on his contributions. If he did this from the £22k over the next five years into a SIPP he could then take that back as a lump sum at 65 and use this to defer taking his state pension for a year or two, which would increase the state pension sum for the rest of his life and this probably makes for a better risk-free return on capital than anything else he could do.