5. Provide your contact details.
You'll be asked if you want HMRC to contact you by phone. If you do, select 'Yes' and input your phone number. If you don't, select 'No'. Regardless of your answer to this question, you'll then be asked whether HMRC can contact you by email. If you're happy with this, select 'Yes' and enter your email address, and if not, select 'No'.
6. You'll see a summary of all the information you've entered – check this is all correct.
Then, click 'Save and continue'. On the next page, you'll be asked to confirm that all the info you've provided is accurate. There's also an option to enter your email address, so you can receive confirmation of your complaint – but you don't have to do this. Click 'Confirm and send' to submit your complaint.
7. You should hear back within 15 days of submitting your complaint.
HMRC will let you know the name and contact details of the person dealing with your complaint. Once it has reviewed your complaint, it'll get in touch to let you know the outcome.
If you're unhappy with the outcome, you'll be told how to ask for a review by email or over the phone. If your case is reviewed and you're still unhappy with the final decision, you can contact the Independent Adjudicator.
If you don't want to complain online, you can contact HMRC over the phone by ringing 0300 200 3100 between 8am and 6pm from Monday to Friday – though be aware that it's likely quicker to submit a complaint online if you're able to do so. Make sure you have your national insurance number to hand.