This article about the renovations at KP say that public and private financing paid for the actual building work, but that the (then) Cambridges paid for their furnishings. According to this article, their apartment was in quite a state of disrepair and was long overdue for upgrades.
This may have been the situation with Royal Lodge, that the repairs and upgrades were deferred, partially because the late QM was overdrawn and didn't want to pay for it and partially because she didn't want to be inconvenienced. The late queen indulged her mother, we know that, so it's believable that she didn't push to have the repairs done during her mother's lifetime. But why wasn't Andrew given the list of repairs and told to have it done by X date as part of his tenancy agreement? Was it Elizabeth indulging her son as she had done her mother? Did he start the process but run out of money?
https://www.housedigest.com/402872/inside-prince-william-and-kate-middletons-stunning-kensington-palace-apartment/
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