Once you know there is a reasonable chance you will bring a claim against a professional, you are encouraged to notify the professional in writing. This letter should contain the following information:
This Preliminary Notice should be sent to the professional and you should ask them to inform their professional indemnity insurers, if they have any, immediately.
The professional should acknowledge the Preliminary Notice in writing within 21 days of receipt. If you are not represented by a solicitor, the acknowledgment should enclose a copy of the Professional Negligence pre-action protocol.
If you do not send any further correspondence to the professional regarding the claim, within 6 months from the date of the preliminary notice, you should notify the professional of your intentions with regard to the claim, i.e. whether you are pursuing the claim, have decided not to pursue it or have yet to reach a decision and, if the latter, when you envisage making a decision.
See here for Step Two – Letter of Claim