Hi Theresa Twigg,
Thank you for your question.
As the cavity wall insulation work was carried out in 2016, under the overpayment relief timeframes found within SACM12005, you are given a four-year window from the end of the relevant tax year or accounting period to claim for expenses.
SACM12005 - Overpayment relief: Overview
For example, if the cavity wall insulation work was carried out in June 2016 during the 2016/2017 tax year, you would have until 5 April 2021 to claim these costs in your Self-Assessment Tax Return.
Currently, working within the four-year timeframe for overpayment relief, any claims prior to the 2019/2020 tax year would now not be eligible to be claimed.
Meaning that unfortunately if further work was carried out within the 2017/2018 or 2018/2019 tax years, the deadline to make any claim would have passed on 5 April 2022 and 5 April 2023 respectively.
If work is carried out on a yearly basis, then you are correct that you may claim the allowance year on year.
We would advise that if you submit your Tax Return online, any costs incurred within the 2021/2022 tax year may be amended online until 31st January 2024.
For previous years 2019/2020 and 2020/2021, we would advise to write into the Self-Assessment queries address found at Self Assessment: general enquiries - GOV.UK (www.gov.uk) highlighting the criteria held under
SACM12150 - Overpayment relief: Form of claims:
Self Assessment: general enquiries
Thank you.