NTMA rates follow the market. They usually announce changes by statutory instrument (S.I.) which can be found on the web. Certificates were last dropped to 5% in June 2016 (issue 22). I was only thinking about this today because 5 year certs in the 22nd issue if purchased in June 2016 will mature in July 2021. Holders of such certs may reinvest in the same issue on maturity if issue 22 is still available. So I'm thinking that the NTMA may swoop in with a change before then. However, we have a bit of Brexit to get through yet!