It seems incredibly short sighted that the benefit you can get from a help to buy ISA was effectively frozen in time at 2015 house prices, when the scheme was devised. Despite the average house price increasing by over £30k in this time, the original limits of £250k and £450k in London still apply. If the the house you buy is over those limits, you get nothing from the scheme. This means the longer you wait and potentially the more you put into the ISA, the less likely it is that you will get any benefit from the account other than the small amount of interest.

So if you have a substantial amount of money in a help to buy ISA you need to carefully consider whether this scheme will be useful for you when you need it, and if not, you probably need to think about putting the money somewhere you will get a better return.