The third provisional payment for the 2017/2018 tax year is due on or by 28 September 2018. This payment is voluntary and you only need to make it if you have underestimated your tax liability for the 2017/2018 year.
However, don’t forget that making this third payment will save you penalties and interest.
Disclaimer: The information provided herein should not be used or relied on as professional advice. No liability can be accepted for any errors or omissions nor for any loss or damage arising from reliance upon any information herein. Always contact your professional adviser for specific and detailed advice.