If you have already enquired about a PPI Claim with Gladstone Brookes:

Note: Your PPI claim starts with a Free PPI Check, our PPI Claim fee of 20% + VAT (so 24%° of the total redress offered by your lender) is payable if your claim is successful. That means if we don’t recover you anything, you don’t pay us a penny

You do not need to use the services of a Claims Management Company like Gladstone Brookes.

You can submit a claim directly to the lender yourself for no charge. You can also approach the Financial Ombudsman Service and Financial Services Compensation Scheme for free to review your case, providing it falls within their remit and you have approached your lender first.